The Tedeschi Trucks Band is like a large-format guitar-centric orchestra of jammy, bluesy Southern rock and soul. (source)
The word "jammy" in the sentence doesn't make a lot of sense to me. The noun "jam" in the context of music refers to a song or a musical piece. By extension "jammy" possibly means "musical"? I can't imagine what a musical band would be. Any band non-musical? All the dictionaries I have checked give "jammy" as "lucky" or "covered in jam", neither of which fit in the context.
Artistic license? Misuse of word?