extracurricular activity / to do something on the side
volunteer activity / to volunteer
internship / to intern
部活動 = club activities
「課外活動」は英訳すると「extracurricular activity」になるけど、「extracurricular activity」は普通に学生について話しに使います。皆の場合には、「do something on the side」を使えます。
I'm an English teacher, but I volunteer on the side.
I just got an internship at a design firm. I'll be working there two days a week.
Do you participate in any volunteer activities?