about perquisite

Perquisite is a benefit or amenity granted at free or concessional cost by an emplyer to an employee, during the course of employment purely on a contractual (employer-employee) basis.

Gratuity also arises out of employment contracts, but is payable  at the time of severence of the contract, in recognition of the past service, contingent upon certain conditions. There may also a nobn-contractual statutory compulsion to pay gratuity.