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1.
Elder member of a band, or band's entourage, who has a significantly greater knowledge or life experience, yet who is still in full support of the musical quest.

Usually the Bandma or Bandpa is old enough to be a grandma or grandpa, but it can also be used in joking to connote a wise-ass, or someone who talks about how old they are.
I wasn't sure if we should do an encore, but Helen, my great "Bandma (or Bandpa)" gave me a wink that said, "go get 'em tiger!"
by Yogoman June 02, 2009