This is the 452nd most frequent Korean word.
끝난
"Finished" or "Ended."
Here, '끝난' acts as an adjective form of the verb '끝나다' (to end) and modifies '수업' (class), indicating that the class has finished.
수업이 끝난 후에 친구들과 카페에 갔습니다.
After the class ended, I went to the cafe with friends.
In this sentence, '끝난' describes '일' (things), emphasizing that these matters have come to an end and suggesting moving past them.
끝난 일을 다시 생각하지 말고 앞으로 나아가세요.
Do not dwell on things that have already ended and move forward.
Here, '끝난' modifies '숙제' (homework), indicating that the homework has been finished or completed.