A rental security deposit is a monetary amount that is paid at the beginning of a rental or lease agreement. The security deposit serves as a protection to the landlord from damage or other failures on the tenant's part, and may also double as an advance on the rent. In the lease agreement, the terms of the security deposit are defined in their own provision. The provision should describe the details by which the security deposit will operate in the lease, including its purpose as a promise against damage, the amount of the deposit and how it was calculated, how the deposit will be used and stored(usually escrow), and lastly, the terms by which the deposit will be returned to the tenant when the lease is over.