"Magic Music Days" is a program at Disney where marching bands, concert bands, and singing groups from middle schools and high schools can come and perform at the parks. Most groups do a performance and then build a two or three day stay around it. The program happens year-round -- on any given day you can see at least one MMD group somewhere on property.
Thanks so much for your replies. My boys are playing in April down there. I had heard that someone was playing the week before them during Magic Music Days. I didn't realize that it was year round. I can't wait to see them perform down there.