The gathering of a specific circle of friends. It is assumed who is coming by the use of the term. It is contrasted with other words and phrases like hanging out, session, cypher, party, which involve a varying degree of sociality and attendance.
Coolfests are reserved usually for those with a common interest or similar inclinations, like humour or music.
(in a text to a friend/s) Coolfest at my place?
We're having a coolfest