A word re-interpreted as an acronym.
[Compound of back + acronym.]
In a backronym, an expansion is invented to treat an existing word as an acronym. An example is the PERL programming language whose name is now explained as an acronym of Practical Extraction and Report Language.
When naming, sometimes a suitable name is chosen and then an acronym is retrofitted on top of it: USA PATRIOT Act (Uniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism). The clunkiness of the expansion is a quick giveaway. How about forming a backronym for ACRONYM itself: A Contrived Result Of Nomenclature Yielding Mechanism?
Often, backronyms serve a useful purpose as mnemonics. For example, see
Apgar Score: http://wordsmith.org/words/apgar_score.html
*yoinked from my A.Word.A.Day e-mail: http://wordsmith.org/awad/