1. noun. A concert/camping festival in Tennessee. Most people think it's about jambands
but the festival covers all music from bluegrass, indie, rock, country, reggae, etc.
2. adjective. Can be used as an expression of something that is really great, groovy, awesome.
As in, holy crap you guys, we are going to have so much fun tonight, rocking out and partying. I am so excited. Let's do it up bonnaroo style. Yeah. Woohoo Bonnarooooooo!