Well, with initials, you pronounce each letter (BO... [bee oh]) but (I'm pretty sure this is the difference) with acronyms, you pronounce all of the letters together as a word. Like hellas said, scuba stands for self contained underwater breathing apparautus, but it is pronounced [skoobah] instead of [ess see you bee ay]. This is my understanding. Therefore, this makes BO and BM initials, not acronyms.
Thank you all, I think I got it. I once saw a lady's T-shirt with these initials, PHD, I was impressed. I thought she might be between jobs after getting her Doctor of Philosophy degree. But there were fine prints below which say professional hairdresser. Funny huh?
Happy Lunar New Year - February 7, the year of the rat.