a security-deposit (caução) is a deposit made into an escrow account for an amount equivalent to three months of rent, payable to the owner in case of late payments or evictions - this is an option usually only available to local residents, and for small units.

the deposit is returned in full at the end of the lease if there is no back-rent due, with accrued interests. 

a collateral bond (título de capitalização) is a financial instrument bought at a local bank for a value established between the landlord and the tenant - the tenants receives interests on the bond during the length of the rental agreement, and the full amount is returned at the end of the lease, while the landlord receives the entire amount of the bond in case of eviction and unpaid rent.