RAS syndrome is the redundant use of one or more of the words that make up an acronym in conjunction with the abbreviated form. This means, in effect, repeating one or more words from the acronym. Three common examples are "PIN number"/"VIN number" and "ATM machine". The term RAS syndrome was coined in 2001 in a light-hearted column in New Scientist.

An acronym, a type of abbreviation, is a word or name consisting of parts of the full name's words. Some authorities add that an acronym must be pronounced as a single word rather than individual letters, so considering NASA an acronym but not USA; the latter they instead call an initialism or alphabetism, for a string of initial letters which are pronounced individually. Acronyms commonly are formed from initials alone, such as NATO, FBI, YMCA, GIF, EMT, and PIN, but sometimes use syllables instead, as in Benelux, NAPOCOR, and TRANSCO. They can also be a mixture, as in radar and MIDAS.