It is a one-time deposit of money given to the landlord at the time of lease signing to ensure that rent will be paid and other responsibilities on the lease are performed. This covers the cost if damage comes to the house/apartment while the tenant is leasing it. Upon the end of a lease, the landlord will assess the damages to the rental unit, take out any charges from the security deposit and return the remaining deposit. The landlord has 21 days from the move out day to return the deposit. Because of Joint and Several liability, the security deposit is only required to be delivered to 1 tenant or co-signer on the lease. Some landlords will honor a request for the money to be divided by all roommates, so if there are 3 tenants on a lease, but this is not a requirement by law.