noun
elective course; special course; non-regular course
Refers to a course that is not part of the regular curriculum, often taken by non-degree students or as an optional subject. Common in university contexts.
彼は大学で選科の授業を取っている。
He is taking an elective course at the university.
選科生として入学する。
Enroll as a non-regular student.
Compound of 選 (select) and 科 (course, department). The exact historical derivation is uncertain, but the meaning is transparent from its components.