Now actually called Ashton Court Festival (which it's been commonly known as, tho it was called Bristol Community Festival in the past), it's a community festival with some international acts (see last years listing for an idea)!
Alongside the music there's films, sculpture, dance, theatre, cabaret, kids area, workshops, and markets.
Car parking is £5 a day. follow AA/RAC signs from motorways/city centre or follow road to Portishead through city.