Mandatory (adjective)

1. Required by law or rule; compulsory.
2. Impossible to avoid or disregard.
3. Binding or compelling.

Origin:

Late middle english (in the sense "having the power to command"): from latin mandatorius, from mandare "to commit to one"s charge", from manus "hand" + dare "to give".

Examples:

1. Wearing a seatbelt is mandatory in this state.
2. The company has a mandatory retirement age of 65.
3. The training is mandatory for all new employees.
4. It is mandatory to attend the meeting.
5. The use of helmets is mandatory for all motorcycle riders.