Without looking it up, I guess that the term 'bacronym' might be a form of Acronym where parts of the words in the Acronym are used, as compared to only the initials. For e.g., if 'HS' was the Acronym for the word 'High Systems', then 'HiSys' might be a bacronym.
Just a very very wild guess, because I didn't look it up, I swear. :-) google is my BFF! :-)