Abbreviations are abbreviated (or shortened) forms of words and phrases. For example, "Mister" becomes "Mr." In writing, abbreviations are generally considered informal. Of course, you will see them in academic texts (as long as you adhere to rule number one), but, by and large, abbreviations are considered an informal form of writing.
Abbreviations allow us to shorten complex words and phrases and be more concise in our writing. The rules for abbreviations are rather complex and can vary. Below, you'll find some of the most important rules and guidelines for using abbreviations in your writing.