abbreviation / acronym / initialism
Three related terms for shortened forms.
An abbreviation is any shortened form of a word or phrase (Dr., etc., oz.). An acronym is an abbreviation read as a word (NASA, NATO, scuba). An initialism is an abbreviation read letter by letter (FBI, HTML, NPR). Use abbreviation when the distinction does not matter. Use acronym only for forms spoken as words.
Examples
UseNASA is an acronym; FBI is an initialism; both are abbreviations.
AvoidFBI is an acronym.
In casual speech many people call every letter-group an acronym. That loose use is widespread, but it blurs a useful distinction. The above is our guidance.