a person who is plays in a band, typically a school band or ensemble. this term is sometimes used as an insult however it is also considered a term of affection as well.
Band nerds can be found in marching bands, pep bands, brass and woodwind ensembles, etc.
A put-down insult used by the untalented people who cannot play instruments intended to somehow "lessen the glory" of the talented, skilled people, but the put-down somehow fails to work every time, contrary to "orch-dorks", a put-down aimed at orchestra people which works every time.
I have to go practice the marimba, chimes, timpani, xylophone, triangle, tabourine, and gong!!!!!! TO THE BAND HALL!!!! dundundundunduuuuuun! (BandNerd Alert!)
Somebody who played in the elementary school band, where it was something everyone did, but was one of those kids who drop it after 1 or 2 years. However, they stay in band anyway because their crush is a band nerd.
Did you hear about Alli? She's only still playing the saxophone just because Aaron is! What a band nerd-faker!