Rental deposit
The rental deposit is a sum paid by the tenant to the landlord when the lease is signed, intended to cover any failings (unpaid rent, damage) at the end of the tenancy.
Its amount is regulated and generally equivalent to several months' rent excluding charges. It is returned to the tenant at the end of the lease, less any justified sums the landlord would be entitled to withhold.
This deposit should not be confused with the first month's rent: it is a separate guarantee, generally held in a separate account for the whole duration of the tenancy.