Compound Acronym
An acronym where each letter is used in a more creative manner to express more meaning than a simpler letter-for-word acronym would enable.
BDSM is technically an acronym, but not a traditional letter-for-word acronym like "TSA" or "LMAO". Instead, the term BDSM acts as a compound acronym. It stands for "Bondage and Discipline, Domination and Submission, Sadism and Masochism". If that term were expressed as a conventional acronym, it would be written out as "BDDSSM", and so consolidating the redundant letters of the acronym and expressing the term as a compound acronym, "BDSM", makes for a term that is far easier to say.