The Backronym reference article from the English Wikipedia on 24-Apr-2004
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Backronym

Helping orphans the way you would do it
A backronym is a word interpreted as an acronym that was not originally so intended. This is a special case of what linguists call back-formation.

"Backronym" is a portmanteau of back and acronym. Discovering backronyms is a common form of wordplay among hackers.

Some examples of backronymns include:

Compare to retronym.