An anacronym is an acronym or an abbreviation so old or familiar that no one remembers what its letters stand for, such as BASIC or COBOL . By the way, an "acronym" is not just any abbreviation. It's a word that is short for other words, usually using their initial letters. An abbreviation formed of letters that don't form a word is sometimes known as an "initialism." Our Webster's cites "snafu" and "radar" as examples of acronyms. (Good examples of anacronyms, too!) But "snafu" and " radar " seem like acronyms that have passed into general usage (notice the all lower case). Most of today's acronyms are still all upper case; only a few will ever become generic. An example of an acronym that probably won't become lower-cased is WINS (Windows Internet Naming Service).
The Webster's definition does raise a question (and begs one, too). Is the "word" an acronym forms a real, already existing word, or intended to be accepted as a new "word," or just something easily pronounceable? If the first case, then "snafu" and "radar" really aren't acronyms. If the second or third case, they are. However, since any initialism can be thought of as a word and certainly has to be pronounceable so you can say it out loud, one could argue that any initialism is an acronym. We don't think anyone has looked at this issue squarely (and we're not planning to ourselves, but just wanted to demonstrate the ambiguous kind of world we live in...which is why most people frankly don't care whether an acronym is a word or not).
But getting back to anacronyms, they seem to be forming at an alarming rate. Do you remember what this mixture of acronyms and initialisms stand for?