the.com/initialism

means A word formed from the first letters of a phrase, where you say each letter aloud instead of blending them into a new pronounceable word (think FBI, not NASA).

from Built straightforwardly from 'initial' (Latin initium, 'beginning') plus the noun-forming suffix '-ism.' The word itself is surprisingly modern as far as grammar terms go, coined in the 20th century specifically to fix a sloppiness in how people used 'acronym' — language mavens wanted a clean label for letter-strings like FBI or USA that sit there, unpronounceable as words, refusing to become NASA or scuba. So the term was built to police the very distinction its own essence jokes about.