A security deposit is a sum of money paid by the tenant at the beginning of a lease that is held by the landlord to cover any damages or unpaid rent at the end of the lease. Rent policies should specify how much the security deposit is, how it will be used, and when it will be returned to the tenant. In some cases, landlords may deduct a portion of the security deposit to cover cleaning or repair costs, so tenants should be sure to document the condition of the property at the beginning and end of the lease to avoid any disputes.