Backronym

occurs in: the etymology and usage section of the Wikipedia article about Rapping

Backronym is a blend of “back” and “acronym”. It describes an existing word that is treated as an acronym and expands its letters into the words of a phrase, even though this phrase does not represent the etymology of the word.

The claim that rap is an acronym for Rhythm And Poetry is a backronym. Similarly, Extraterrestrial Publishing is a backronym for XPUB!