Single letters that stand for a phrase?

Single letters that stand for a phrase are often referred to as acronyms or initialisms. In an acronym, the first letters of each Word in a phrase are combined to create a new Word, such as "NATO" for North Atlantic Treaty Organization. An initialism, on the other hand, uses the first letters but is pronounced letter by letter, like "FBI" for Federal Bureau of Investigation. These linguistic tools are commonly used to simplify longer phrases for easier communication.