The small square literally stands for QED, we just use the symbol for shorthand it isn't a replacement.
These answers are technically not acronyms because the three letters don't make a new word. Examples of true acronyms are 'Agents of SHIELD', 'Enter your PIN' or 'I work for NASA'. Technically, when you say each letter individually, they're initialisations. I say *technically* because English evolves - it's not like French which is officially governed. I like to use the word 'moot' as an example: everyone uses it to mean the opposite of what it actually means (a redundant point, instead of worthy of debate), progressively changing the actual definition.
People like Roleybob just like to troll to make themselves feel smarter than other jetpunkers.
I seldom hear the term "fewer than" used anymore. It has almost universally been replaced by "less than". WHY?