Drop in - Tradução em português

In this video
Steve Jobs says (at 01:01): I dropped out of Reed College after the first six months but then stayed around as a drop-in for another eighteen months or so before I really quit.

I know that "drop out" can mean "largar a faculdade", but, what about "drop in"? Is the latest used just when somebody dropped out of college and then returned back? Or it can be also applied to a person who just entered the college?

Thank you very much indeed!