selective system; system with choices
Refers to a system where participants can choose from multiple options, such as elective courses in education or choice-based plans in services.
At this school, school lunch is on a selective system.
It's fun to choose elective subjects.
必修 means compulsory or required, often contrasted with 選択制 in educational contexts.
Compound of 選択 (choice) and 制 (system).