Dudelive in the Happy Easter thread mentioned a term most of us might have already knew, but I didn't see it listed above.
@BigDadday -
Did you want to add that term to your nice list?
Easter egg, n.
1. A message hidden in the object code of a program as a joke, intended to be found by persons disassembling or browsing the code. 2. A message, graphic, or sound effect emitted by a program ... in response to some undocumented set of commands or keystrokes, intended as a joke, to display program credits or just to do something special not mentioned about anywhere else.