There are a number of music camps already entered: https://musicbrainz.org/tag/music%20camp (incl. a bunch that aren't tagged as such). Music camps are common in at least marching band music ("band camps"), classical music, and folk music.

They're different from festivals in that the focus is not on more or less passively watching someone else perform.
They're different from master classes in that it isn't a single class. A music camp will commonly have a number a of workshops and/or master classes.
They're different from convention/expos in that they are centered around music and musical performance and, like with festivals, that the focus isn't on the people attending the event "passively" receiving music, but actively participating in improving their own musicianship.

Maybe a broader term than "music camp" can be used though, as there may be eligible dance or other "art and performing art" camps that, for the sake of MusicBrainz, would fall somewhere between "music camp" (in being for the advancement of the participants) but while not being a music camp, it might still have a concert or other musical event(s) embedded in it.

https://en.wikipedia.org/wiki/Band_camp
https://en.wikipedia.org/wiki/Summer_camp#Art_and_performing_art_camps