Dear Tribikram,
"Ex-gratia" is Latin (lit. 'by favour') and is most often used in a legal context. When something has been done ex gratia, it has been done voluntarily, out of kindness, or grace. In law, an ex gratia payment is a payment made without the giver recognizing any liability or legal obligation.
In most cases, ex-gratia is paid along with the annual bonus. Since the Payment of Bonus Act puts a cap on a 20% bonus for employees, the employer and employee agree to pay a higher amount than 20% and coined a new term, ex-gratia, which is paid along with the bonus.
Rgds,
Suresh Ramalingam
Consultant - Compliance