noun
special student; non-matriculated student; non-regular student
Refers to a student who takes courses at a school or university without being formally enrolled in a degree program; often used in the context of auditing classes or taking individual subjects.
彼は選科生として大学の授業を受けている。
He is taking university classes as a non-matriculated student.
選科生でも図書館を利用できますか。
Can non-regular students also use the library?
正規生 is a regular, matriculated student enrolled in a degree program, contrasting with the non-regular status of 選科生.
Compound of 選科 (senka, 'selected course') + 生 (sei, 'student'). The term is straightforward and its meaning is transparent from its components.