typically the small orange skinned, green haired fellows that devote their lives to floating on the chocolate river or picking gumdrops off of the gumdrop trees
if particularly band-nerdy, it means the part in a song (usually march) in which the tubas take the down-beat and the horns take the up-beat, thus creating an OOMPA SOUND
(and as a result, the ham song is born)
"oompa loompa doompadee do, i've got another story for you."
"don't touch the chocolate river!!!"
band director- "cmon horns,i need that oompa effect!!!!"