A party, open to many, where drugs are very available.

Literally, the verb 'rave' means to go mad, or to behave as if you were mad. However, nowadays it's usually used to describe someone being very enthusiastic about something. eg Everyone's raving about the new Spanish restaurant in town. This means that everyone is saying how fantastic it is. or Q: 'What did you think of that book?' A: 'Hmm, it was ok, but nothing to rave about.' It's particularly used when talking about reviews, and can even be used as an adjective. The band's new album had rave reviews.

We need to see it in a sentence, to know how to answer your question. Susan is right about the "party" meaning, but the verb "to rave" has several meanings that are not related to "raves" as parties.