Mandatory means required, not optional. When something is mandatory, you must do it, whether you want to or not. Schools make certain vaccinations mandatory to protect everyone's health. A workplace might make safety training mandatory for all employees. When attendance is mandatory, you can't just skip it because you'd rather do something else.

The opposite of mandatory is optional or voluntary: something you can choose to do or not do. A mandatory book report has to be completed. An optional extra credit project is up to you.

When something is mandatory, it carries the weight of a command, not a suggestion. Your parents might make homework mandatory before screen time. A coach might make practice attendance mandatory during the season.

You'll often see mandatory paired with words like requirement, attendance, or training. Sometimes people use compulsory to mean nearly the same thing, though mandatory is more common in everyday speech. Understanding what's mandatory helps you know which rules you must follow and which activities are truly up to you.