Yes, it means fraternities and sororities. I suggest you just look up a Wikipedia entry or Google it for a full explanation. Basically, it’s a way for like-minded people to form a very close network of friends who do a lot of stuff together. It can have negative or positive results, depending on who you talk to and what news stories you read. Some colleges have very active Greek life where the majority of students participate, other colleges have none at all. At some colleges they all live together in their own frat or sorority houses, at other colleges it’s more like a club that hosts parties and events.
Some colleges with a lot of Greek life have bad reputations for being full of hard-partying students who do disgraceful things, other colleges have greek groups that do many good things for both the college and the community. There is a LOT of variation. My kid wanted as little Greek life on campus as possible and only looked at colleges that had 30% or below participation in Greek life. It is often associated with a lot of drinking and partying.