Abbreviations and contractions are both used to shorten a word, but in different ways.
An abbreviation is formed using the initial letters (or sometimes other parts) of a longer word or phrase to represent the whole. Common examples include “Mr.” for “Mister,” “Dr.” for “Doctor,” and “NASA” for “National Aeronautics and Space Administration.” They are used in formal writing as well as everyday conversations.
A contraction, on the other hand, is formed by combining two words and omitting one or more letters. The deleted letters are replaced with an apostrophe (e.g., “cannot” becomes “can’t”). Contractions are commonly used in spoken and informal written English.