The document defines an acronym as a word formed from the initial letters of words or phrases. Acronyms are used to make language more concise for speaking or writing. While abbreviations shorten words or phrases, acronyms use the first letters of each word to form a new word. Some examples of common acronyms provided are GPS, ADSL, CIA, and UNICEF. The document explains that acronyms are used for convenience to allow for faster speaking and writing.