Yulan Real Estate Lawyer, New York

A doctrine that prevents a defendant from re-litigating an issue after it has been lost. For example, if your neighbor sues you for putting up a fence on his land and the court rules that your fence extends beyond your property line, you can't later file your own lawsuit seeking a declaration that the property line is incorrectly drawn.

The loss of property or a privilege due to breaking a law. For example, a landlord may forfeit his or her property to the federal or state government if the landlord knows it is a drug-dealing site but fails to stop the illegal activity. Or, you may have to forfeit your driver's license if you commit too many moving violations or are convicted of driving under the influence of alcohol or drugs.

In a contract, a promise by one party not to hold the other party responsible if the other party carries out the contract in a way that causes damage to the first party. For example, many leases include a hold harmless clause in which the tenant agrees not to sue the landlord if the tenant is injured due to the landlord's failure to maintain the premises. In most states, these clauses are illegal in residential tenancies, but may be upheld in commercial settings.

The many types of information presented to a judge or jury designed to convince them of the truth or falsity of key facts. Evidence typically includes testimony of witnesses, documents, photographs, items of damaged property, government records, videos and laboratory reports. Rules that are as strict as they are quirky and technical govern what types of evidence can be properly admitted as part of a trial. For example, the hearsay rule purports to prevent secondhand testimony of the 'he said, she said' variety, but the existence of dozens of exceptions often means that hairsplitting lawyers can find a way to introduce such testimony into evidence. See also admissible evidence, inadmissible evidence.

Laws that limit the amount of rent landlords may charge, and that state when and by how much the rent can be raised. Most rent control laws also require a landlord to provide a good reason, such as repeatedly late rent, for evicting a tenant. Rent control exists in some cities and counties in California, Maryland, New Jersey, New York and Washington, D.C.

A request made to a court, asking it to dismiss a lawsuit on the grounds that no legal claim is asserted. For example, you might file a demurrer if your neighbor sued you for parking on the street in front of her house. Your parking habits may annoy your neighbor, but the curb is public property and parking there doesn't cause any harm recognized by the law. After a demurrer is filed, the judge holds a hearing at which both sides can make their arguments about the matter. The judge may dismiss all or part of the lawsuit, or may allow the party who filed the lawsuit to amend its complaint. In some states and in federal court, the term demurrer has been replaced by 'motion to dismiss for failure to state a claim' (called a '12(b)(6) motion' in federal court) or similar term.

An extraordinary and unexpected natural event, such as a hurricane, tornado, earthquake or even the sudden death of a person. An act of God may be a defense against liability for injuries or damages. Under the law of contracts, an act of God often serves as a valid excuse if one of the parties to the contract is unable to fulfill his or her duties -- for instance, completing a construction project on time.

A legally binding contract in which a person or business promises to treat specific information as a trade secret and not disclose it to others without proper authorization. Nondisclosure agreements are often used when a business discloses a trade secret to another person or business for such purposes as development, marketing, evaluation or securing financial backing. Although nondisclosure agreements are usually in the form of written contracts, they may also be implied if the context of a business relationship suggests that the parties intended to make an agreement. For example, a business that conducts patent searches for inventors is expected to keep information about the invention secret, even if no written agreement is signed, because the nature of the business is to deal in confidential information.