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.