A “security deposit” is an amount of money the tenant gives to the landlord when the tenancy begins. What it covers depends on what the agreement (oral or written) says about it.
It might cover unpaid rent, damage to the premises, or cleaning charges. People often get into fights about security deposits because the original agreement was too vague. If the agreement says “for cleaning”, ask the landlord to write down clearly what “cleaning” means.
Does it include cleaning the oven? Shampooing the carpet? Dry-cleaning the drapes? Automatically, or only if these things are dirty? Spell it out to save everyone a lot of grief later. And check out the premises when you first move in to see if there is any damage caused by prior tenants. If so, write it on the agreement so you don’t get charged for it.