FBI. CDC. AOL. DOJ. Read just about anything today and you’ll find an acronym – or at least an initialism. (An acronym is an abbreviation that’s pronounced as one or more words. An initialism just goes purely by the letters.) Sometimes these abbreviations are well-known. For example, everybody knows what “FBI” stands for, and what the letters “IRS” stand for (do note, though, that when you put ‘the’ and ‘irs’ together, it spells ‘theirs’). But some acronyms and initialisms are taken for granted, while at the same time remain unknown as to what the letters stand for. See how many of these YDK (you do know).