outdoor music festival
Abbreviation of 野外フェスティバル. Refers specifically to music festivals held outdoors, often multi-day events with camping.
See also: 野外フェスティバル
This year's outdoor music festival will be held for three days.
If you're going to an outdoor music festival, you'd better bring rain gear.
Clipping of 野外フェスティバル (outdoor festival), itself a compound of 野外 (outdoors) and フェスティバル (festival).