students' association; alumni association
Refers to an organization of current students or graduates of a school. The exact meaning depends on the institution; some 学友会 are student councils, while others function as alumni networks.
He serves as treasurer in the university's students' association.
Even after graduation, I attend gatherings of the alumni association.
生徒会 is a student council in a school, typically for current students, whereas 学友会 may include alumni or be used in university contexts.
Compound of 学 (learning, school), 友 (friend), and 会 (association). The term is a straightforward Sino-Japanese formation.