Festivals are concerts with amplitude and, sometimes, attitude.
Most festivals are family oriented, a canny combination of art, frolic, and information. For instance, you may be at a blues festival, but over the course of the day, you'll probably hear a raucous mix of acoustic or electric instrumentation, strains of Chicago, Texas, or Mississippi Delta blues, performed by venerated elders and young pups. And festivals by their very nature encourage jams, both onstage and off. In fact, some folks never see an onstage performance at a bluegrass festival. They go to play rather than to listen.