The period when someone was a student; refers to one's school days (elementary, middle, high school, university) and related experiences.
学生時代はサッカー部に所属していました。
I belonged to the soccer club during my student days.
あの先生とは学生時代からの友人です。
That teacher has been a friend of mine since my school days.
学生時代の写真を見て懐かしくなった。
Looking at photos from my school days made me feel nostalgic.