One's alma mater — the school one graduated from or formerly attended.
今年は母校の創立100周年で、同窓会に参加した。
This year marks the 100th anniversary of my alma mater, and I attended the alumni reunion.
休みの間に母校を訪れて、恩師に挨拶した。
During the holiday I visited my alma mater and greeted my former teacher.
母校の図書館は学生の時と比べてずいぶん変わった。
The library at my alma mater has changed a lot compared to when I was a student.