Gratuity is a certain amount paid by an employer to an employee as gratitude for serving over 5 years. It is applicable when an employee reaches retirement age, resigns after 5 years of service, dies, or becomes disabled. Gratuity in India can be calculated using the formula: Gratuity = [{Salary / 26} x 15 days x Number of years of service], where salary includes basic pay and dearness allowance, 26 are the number of working days in a month, and 15 days is the salary amount. The document provides steps to use an online gratuity calculator to easily calculate this benefit.