What is a abbreviations?

An abbreviation is a shortened version of a word.
Example: MBA = Masters in Business Administration.
MBA is an abbreviation.
Isn't and aren't are contractions but could technically be called abbreviations because the apostrophes replace one or two letters. "Assoc." is an abbreviation for association. USA is and abbreviation for the United States of America and UK is an abbreviation for the United Kingdom. No. is an abbreviation for number. Usually any word with a full stop directly after it is an abbreviation (unless it is at the end of a sentence...) Hope this helps :)