Hoffmeister Land Use & Zoning Lawyer, New York

An unforeseen and uncontrollable event that excuses a party to a contract from performing his or her duties under that contract. For example, a landlord can break a lease if the property she agreed to rent accidentally burns down before the tenants move in.

Any control over property. If you give away property but keep an incident of ownership--for example, you give away an apartment building but retain the right to receive rent--then legally, no gift has been made. This distinction can be important if you're making large gifts to reduce your eventual estate tax.

A promise that pledges nothing, because it is vague or because the promisor can choose whether or not to honor it. Such promises are not legally binding. For example, if you get a new job and promise to work for three years, unless you resign sooner, you haven't made a valid contract and can resign or be fired at any time.

A sale of a house in which the proceeds fall short of what the owner still owes on the mortgage. Many lenders will agree to accept the proceeds of a short sale and forgive the rest of what is owed on the mortgage when the owner cannot make the mortgage payments. By accepting a short sale, the lender can avoid a lengthy and costly foreclosure, and the owner is able to pay off the loan for less than what he owes. See also deed in lieu (or foreclosure).

A valid contract in which a copyright owner authorizes another person or entity (called the licensee) to exclusively exercise one or more of the rights (or portion of such rights) that belong to the copyright owner under the copyright. The licensee is said to 'own' the rights granted in the license and is referred to as a copyright owner.

Principles of international law so fundamental that no nation may ignore them or attempt to contract out of them through treaties. For example, genocide and participating in a slave trade are thought to be jus cogens.

A large final payment due at the end of a loan, typically a home or car loan, to pay off the amount your monthly payments didn't cover. Many states prohibit balloon payments in loans for goods or services that are primarily for personal, family or household use, or require the lender to let you refinance the balloon payment before forcing collection.