Leaving or dropping out of school; formally quitting attendance (often used as 'to drop out').
家庭の事情で彼は高校を退学した。
He dropped out of high school due to family circumstances.
学費が払えず、大学を退学せざるを得なかった。
Unable to pay tuition, I had no choice but to drop out of university.
退学を決める前に、必ず相談窓口に連絡してください。
Before deciding to drop out, be sure to contact the counseling office.
Expulsion from school; dismissal imposed by the institution (e.g., for disciplinary reasons).
暴力行為が発覚し、彼は退学処分を受けた。
His violent behavior was discovered and he was expelled from school.
退学処分になる前に、事実確認が行われるべきだ。
There should be a fact-finding process before expulsion is imposed.
Dated usage: leaving a school after completing a course (an older sense).
古い記録によれば、彼は学位を得て退学したとある。
According to old records, he left the school after receiving his degree.