Here are some examples of how "compulsory" can be used:
* "Compulsory education" refers to the requirement for children to attend school until a certain age.
* "Compulsory military service" means that citizens are required to serve in the armed forces for a period of time.
* "Compulsory voting" refers to a system where citizens are required to vote in elections.
The word "compulsory" implies that there is no choice in the matter. If something is compulsory, you have to do it.