All terms

Legal Terms: M

Federal & State Law Editorial TeamLast reviewed: April 2026
M'Naghten Rulecriminal procedure

The traditional cognitive test for insanity, asking whether the defendant knew the nature of the act or that it was wrong.

The Modified Accelerated Cost Recovery System under IRC Section 168, the primary federal depreciation method for most tangible property placed in service after 1986, with prescribed recovery periods and methods.

A judicial officer with limited authority, often handling preliminary criminal proceedings, minor offenses, and pretrial matters.

Mailbox Rulecontract law

The default rule that acceptance is effective upon dispatch (e.g., mailing), while revocations, rejections, and counteroffers are effective on receipt.

Main Purpose Rulecontract law

An exception removing a suretyship promise from the statute of frauds when the surety's main purpose is to advance its own economic interest.

A federal statute granting federal courts jurisdiction over certain serious crimes committed by Indians in Indian country.

Wrongful conduct or illegal activity, especially by a public official.

Malingeringcriminal procedure

The intentional fabrication or exaggeration of physical or mental symptoms, often to avoid prosecution or punishment, distinguished from genuine illness.

Professional negligence — the failure of a professional (doctor, lawyer, accountant) to meet the standard of care, resulting in harm to the client or patient.

An LLC in which management authority is vested in one or more designated managers (who may or may not be members), while non-managing members function more like passive investors. This structure is common when there are passive investors or large numbers of members.

Mandamuscivil procedure

A court order compelling a government official or entity to perform a mandatory duty.

Mandamuscivil procedure

An extraordinary writ from a superior court commanding a public official or lower court to perform a clear, non-discretionary duty.

Mandatecivil procedure

An official order or command from a court, especially an appellate court directing a lower court to take specific action.

Mandatory Minimumcriminal procedure

A statutorily required minimum sentence that the court must impose upon conviction, regardless of mitigating factors.

A redemption right that the company is obligated to fulfill on a fixed date or upon specified events, often resembling a debt instrument from a balance-sheet perspective.

Manslaughtercriminal

The unlawful killing of a person without premeditation or malice aforethought. Can be voluntary (in the heat of passion) or involuntary (through criminal negligence).

Marginsecurities

Borrowed money used to purchase securities, subject to Regulation T and maintenance requirements set by the Federal Reserve and FINRA.

The tax rate applied to the next dollar of income, determined by which bracket that dollar falls into in the progressive rate schedule.

An unlimited estate and gift tax deduction for transfers to a U.S. citizen spouse under IRC Sections 2056 and 2523, effectively deferring transfer tax until the surviving spouse's death.

Two related privileges: testimonial privilege barring spousal testimony in criminal cases, and confidential communications privilege protecting marital communications.

Property acquired during a marriage that is subject to division upon divorce, as opposed to separate property.

Assets and debts acquired by either spouse during the marriage, regardless of how titled, that are subject to division in a divorce under either equitable distribution or community property rules.

Artificial inflation or deflation of a security's price through deceptive trading practices such as wash trading, spoofing, or pump-and-dump schemes.

A pretrial hearing in patent litigation where the court construes the meaning and scope of disputed patent claim terms.

Markman Hearingintellectual property

A pretrial hearing in patent litigation at which the court construes the meaning of disputed claim terms, named after Markman v. Westview Instruments (1996).

The initial preliminary appearance in immigration court at which the noncitizen pleads to the allegations in the Notice to Appear, identifies any applications for relief, and receives scheduling for individual merits hearings.

Material Factcivil procedure

A fact that, under the governing substantive law, could affect the outcome of the case and therefore can preclude summary judgment if genuinely disputed.

A false statement of fact that is significant enough to influence an investor's decision to buy, sell, or hold a security.

Information about a company that has not been made available to the general public and would likely affect the company's stock price if disclosed.

Active and regular involvement in a trade or business activity on a substantial basis, measured by seven tests in the Section 469 regulations, that allows losses to escape passive limitations.

A witness whose testimony is important enough to a case that they may be detained to ensure their availability.

The highest level of a contaminant allowed in drinking water under the Safe Drinking Water Act, enforceable by the EPA.

McQuiggin v Perkinscriminal procedure

A 2013 Supreme Court decision recognizing that a credible showing of actual innocence may excuse AEDPA's statute of limitations in habeas cases.

Means Testbankruptcy

A formula used in Chapter 7 bankruptcy to determine whether a debtor's income is low enough to file for Chapter 7 or whether they must file under Chapter 13.

A patent claim element described by the function it performs rather than the specific structure, interpreted to cover the corresponding structure disclosed in the specification and its equivalents.

Mechanic's Lienreal estate

A statutory lien placed on real property by a contractor, subcontractor, or material supplier who has not been paid for work performed or materials furnished.

Mediationcivil procedure

A form of alternative dispute resolution where a neutral third party facilitates negotiation between the parties to help them reach a voluntary agreement.

Mediationcivil procedure

A consensual dispute resolution process in which a neutral third party assists the disputants in reaching a voluntary settlement, without the power to impose a decision.

Mediationfamily law

A voluntary or court-ordered process in which a neutral third party helps separating spouses negotiate agreements on custody, support, and property without imposing a decision.

Medicaidhealthcare

A joint federal-state program providing health insurance coverage to low-income individuals and families, with eligibility and benefits varying by state.

Professional negligence by a healthcare provider in which treatment falls below the accepted standard of care and causes injury or death to the patient.

Medicarehealthcare

A federal health insurance program primarily for individuals aged 65 and older, consisting of Part A (hospital), Part B (medical), Part C (Medicare Advantage), and Part D (prescription drugs).

Melson Formulafamily law

A child-support calculation method used by Delaware, Hawaii, and Montana that first reserves a self-support amount for each parent before allocating remaining income to the child's needs.

An LLC in which all members participate directly in the day-to-day management and decision-making of the company, with each member generally having authority to bind the LLC. This is the default structure in most states unless the operating agreement provides otherwise.

Mens Reacriminal

Latin for 'guilty mind.' The mental state or intent required to establish criminal liability, such as intent, knowledge, recklessness, or negligence.

Mens Reacriminal procedure

The mental state or guilty mind required to establish criminal liability, ranging from purposeful intent to negligence. The Model Penal Code recognizes four levels: purposely, knowingly, recklessly, and negligently.

The principle that most crimes require proof of a guilty mental state, such as intent, knowledge, recklessness, or negligence.

Federal and state laws requiring health insurers to provide mental health and substance use disorder benefits comparable to medical and surgical benefits.

Mergerbusiness

The combination of two or more companies into a single entity. In contract law, the integration of prior agreements into a final written contract.

Mergerbusiness

A corporate combination in which one entity is absorbed into another or two entities combine into a new entity, with the surviving entity assuming the assets and liabilities of the constituents by operation of law.

Merger Doctrinecriminal procedure

The principle that lesser-included offenses merge into the greater offense for conviction, preventing multiple punishments for the same conduct.

The process of discharging a service member from the military outside of the court-martial system, for reasons such as misconduct, performance deficiencies, or medical conditions.

A court within each branch of the armed forces that reviews court-martial convictions and sentences for legal errors.

A tribunal convened to try individuals for violations of the law of war and related offenses, distinct from courts-martial that try service members.

A federal statute extending U.S. criminal jurisdiction to certain civilians and contractors accompanying the armed forces overseas.

A judge advocate certified to preside over courts-martial, ruling on questions of law, instructing panel members, and imposing sentences.

An order issued by a military commander directing a service member to refrain from contact with a specified person, similar to a civilian restraining order.

Rules governing the admissibility of evidence in courts-martial, adapted from the Federal Rules of Evidence with modifications specific to military proceedings.

The constitutional requirement that a defendant must have sufficient connections with a forum state before the state's courts can exercise personal jurisdiction.

Minimum Contactscivil procedure

The constitutional standard from International Shoe v. Washington (1945) requiring sufficient connections with the forum so that suit does not offend traditional notions of fair play and substantial justice.

A HIPAA requirement that covered entities limit the use, disclosure, and request of protected health information to the minimum amount needed to accomplish the intended purpose.

Minorfamily

A person who has not yet reached the age of legal majority (typically 18) and lacks full legal capacity.

The rights that law enforcement must inform a suspect of upon arrest and before custodial interrogation, including the right to remain silent and the right to an attorney.

Miranda Rightscriminal procedure

The constitutional protections recognized in Miranda v. Arizona (1966), including the right to remain silent, to have counsel present, and to appointed counsel if indigent.

Miranda Warningcriminal procedure

The advisement police must give a suspect before custodial interrogation, informing them of the right to remain silent and to counsel. Failure to administer it generally bars use of resulting statements.

Mirror Image Rulecontract law

The common-law principle that an acceptance must match the terms of the offer exactly, with any deviation constituting a counteroffer rather than acceptance.

The incorrect classification of an employee as an independent contractor, potentially depriving the worker of benefits, protections, and proper tax treatment.

Misdemeanorcriminal

A criminal offense less serious than a felony, typically punishable by fines, probation, or imprisonment for up to one year.

Misprisioncriminal

The crime of concealing knowledge of a felony or an act of treason from authorities.

A false statement of material fact made to induce another party to enter into a contract or transaction.

Misrepresentationcontract law

An assertion not in accord with the facts, which may be fraudulent, negligent, or innocent and may render a contract voidable by the misled party.

Mistakecontract law

An erroneous belief about a material fact existing at the time of contracting, which may render the contract voidable depending on whether it was mutual or unilateral.

Mistake of Factcriminal procedure

A defense negating mens rea when the defendant held an honest, and sometimes reasonable, belief about a fact that, if true, would make the conduct lawful.

Mistake of Factcontract law

An erroneous belief about a present or past fact, distinguishable from a mistaken prediction about the future and generally a stronger basis for relief than mistake of law.

Mistake of Lawcriminal procedure

A defense rarely accepted in criminal law, holding that ignorance or misunderstanding of the law generally does not excuse criminal conduct.

Mistake of Lawcontract law

An erroneous belief about the legal effect of facts, historically not a ground for relief but increasingly recognized under the modern Restatement approach.

Mistrialcriminal

A trial that has been terminated before its conclusion due to a procedural error, hung jury, or other extraordinary circumstance.

Mitigationgeneral

The duty of an injured party to take reasonable steps to minimize their damages. Also, factors presented at sentencing to argue for a lighter punishment.

Mitigationcontract law

The duty of the non-breaching party to take reasonable steps to limit its losses after a breach, with avoidable damages not recoverable.

Modificationcontract law

A change in the terms of an existing contract, which under the common law requires new consideration but under UCC 2-209 needs only good faith.

A distinctive pattern of criminal conduct so unique that it identifies the defendant as the perpetrator, admissible under FRE 404(b).

Monopolybusiness

Exclusive control of a market by a single entity, which may violate federal antitrust laws if achieved through anticompetitive practices.

Mootcivil procedure

A legal issue that has become academic or no longer presents a live controversy, making judicial resolution unnecessary.

An act or behavior that violates community standards of justice, honesty, or good morals. Crimes involving moral turpitude can affect immigration status.

Mortgageproperty

A loan secured by real property, where the borrower grants the lender a security interest in the property until the loan is repaid.

Mortgagereal estate

A legal instrument giving a lender a security interest in real property as collateral for a loan, with the borrower retaining possession.

The itemized deduction for interest paid on acquisition indebtedness secured by a qualified residence, capped at $750,000 of principal for loans originated after December 15, 2017.

Motioncivil procedure

A formal request made to a court asking for a ruling or order on a specific issue.

A post-answer motion under Rule 12(c) seeking judgment based solely on the pleadings, evaluated under the same standard as a Rule 12(b)(6) motion.

Motion for New Trialcivil procedure

A post-verdict motion under Rule 59 seeking a new trial on grounds such as erroneous evidentiary rulings, jury misconduct, or verdict against the weight of the evidence.

A pretrial motion under Rule 56 seeking judgment as a matter of law when there is no genuine dispute of material fact.

Motion in Liminecriminal procedure

A pretrial motion seeking an evidentiary ruling, typically to exclude prejudicial or inadmissible evidence before it is offered at trial.

Motion to Compelcivil procedure

A request under Rule 37(a) for a court order requiring an opposing party or non-party to respond to discovery requests after a good faith conference fails.

Motion to Dismisscivil procedure

A motion asking the court to dismiss a case for legal insufficiency, such as failure to state a claim or lack of jurisdiction.

Motion to Dismisscivil procedure

A pretrial motion under Rule 12(b) seeking dismissal on grounds such as lack of jurisdiction, improper venue, defective service, or failure to state a claim.

Motion to Quashcivil procedure

A request to invalidate a subpoena, typically under Rule 45(d), on grounds such as undue burden, privilege, or geographical limits.

A request under Rule 55(c) to vacate an entry of default for good cause, or to set aside a default judgment under the stricter standards of Rule 60(b).

Motion to Suppresscriminal procedure

A pretrial motion seeking exclusion of evidence allegedly obtained in violation of the defendant's constitutional rights.

Motion to Transfercivil procedure

A request under 28 USC 1404(a) to move a properly filed federal action to another district where it could have been brought, for convenience and the interests of justice.

Motiveevidence

A non-propensity purpose for which prior bad acts may be admitted, showing the defendant had a reason to commit the charged offense.

Move-Away Casefamily law

A contested proceeding addressing a custodial parent's proposed relocation, in which the court weighs the relocating parent's reasons, the impact on the child, and the feasibility of preserving the non-moving parent's relationship.

Murdercriminal

The unlawful killing of a person with malice aforethought (premeditation and deliberation). First-degree murder involves planning; second-degree murder does not.

Mutual Mistakecontract law

A shared erroneous belief of both parties about a basic assumption of the contract that materially affects the agreed exchange, generally rendering the contract voidable.

Mutuality of Estoppelcivil procedure

The historical requirement that issue preclusion be available only between parties bound by the prior judgment, largely abandoned in modern federal practice.

MVRAcriminal procedure

The Mandatory Victims Restitution Act of 1996, requiring restitution in specified federal offenses regardless of the defendant's ability to pay.

MY LEGS Exceptionscontract law

A mnemonic for contracts within the statute of frauds: Marriage, contracts not performable within one Year, Land, Executor promises, Goods over $500, and Suretyship.

This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.