Most leases and rental agreements require tenants to pay a deposit (the amount is usually a month or two of rent) before moving in. This is typically in addition to first month's rent and fees (such as for parking) that some landlords charge.
If a tenant damages the property or leaves early owing rent, the landlord can use the deposit to cover what the tenant owes.
State security deposit laws provide specific details as to the maximum amount of the deposit, how it may be used, when it must be returned (and whether or not interest is required), and tenant rights if the landlord violates the law. A tenant may sue a landlord in small claims court for failure to return the deposit (usually the tenant must first send the landlord a demand letter).