elective subject; elective course
Refers to a subject or course that students can choose to take, as opposed to a required one. Used in school and university settings.
I plan to take psychology as an elective next semester.
この大学では、選択科目の幅が広い。
This university offers a wide range of elective courses.
She is taking French as an elective.
Please choose one from among the elective subjects.