n. a payment required by a landlord from a tenant to cover the expenses of any repairs of damages to the premises greater than normal "wear and tear." The security deposit must be returned within a short time (varying by states) after the tenant vacates, less the cost of repairing any unusual damage. Unfortunately for tenants, these damages are usually subject to the judgment of the landlord, who may desire to paint and refinish on the tenant's money, which results in many small claims suits. In a few states the security deposit must be kept in a separate bank account, and some states require payment of interest on the amount held as a deposit. A security deposit is sometimes confused with a deposit of the "last month's rent," which may be credited to the tenant for the final month's rent. A security deposit cannot be used legally as a rent credit. See also: landlord and tenant lease rent

A security deposit is a sum of money held in trust either as an initial part-payment in a purchasing process (often used to prevent the seller's selling an item to someone else during an agreed period of time while the buyer verifies the suitability of the item, or arranges finance), also known as an earnest payment, or else, in the course of a rental agreement to ensure the property owner against default by the tenant and for the cost of repair in relation to any damage explicitly specified in the lease and that did in fact occur.

The Knightsbridge Security Deposit robbery took place on 12 July 1987 in Cheval Place, Knightsbridge, England, part of the City of Westminster in London. This robbery, the Banco Central burglary at Fortaleza, and the $900 million stolen from the Central Bank of Iraq in 2003 are said to be the largest bank robberies in history.