When An Organization Has Letters As A Name, Like CIA Or FBI What Is That Called?

Most people call this an acronym. Some purists insist that the word acronym should be confined to cases where the first letters combine together to form a word, as in P.A.T.R.I.O.T. Act, or where, at the very least, the letters are pronounced in a way that is different from just the sequence of letters, for example AIDS. According to this view, examples like CIA or FBI should instead be called alphabetisms or initialisms.