Mandatory/ˈmændətɔːri/ Definition 1 of 3Pro Tip 1/3Beyond Laws Mandatory isn't used only for laws but for rules in organizations, schools, or clubs. Attendance is mandatory for all members at the club meetings. Pro Tip 2/3Safety Related 'Mandatory' is often used in safety contexts to mean 'necessary for safety'. It's mandatory to wash your hands before serving food. Pro Tip 3/3Not Optional When something is mandatory, you cannot choose whether to follow it or not. Completing this course is mandatory for graduation.