RAS Syndrome refers to the unnecessary redundancy of certain acronyms. The acronym "RAS" stands for Redundant Acronym Syndrome, so the term "RAS Syndrome" incorporates the linguistically odd use of an acronym that is followed by one of the words that it shortens, which is exactly what the term describes. In essence, "RAS Syndrome" means Redundant Acronym Syndrome Syndrome. An example of a term that suffers from RAS Syndrome is "PIN number," which essentially means Personal Identification Number number.
This concept was first explained by New Scientist magazine in 2001. Acronyms are supposed to shorten a phrase for ease of use, but people occasionally add words to acronym for common parlance. The syndrome occurs when the word that is added on is one of the words that the acronym was supposed to shorten in the first place, as in RAS Syndrome or PIN number.
Other occurrences of RAS Syndrome in the English language include common references to automated teller machines as "ATM machines," alternating current as "AC current," direct current as "DC current" and individual retirement accounts as "IRA accounts." In each case, the word that is added to the acronym is also represented by the last letter in the acronym. In some cases, more than one words might be added despite their first letters being in the acronym already. One example is an emergency position-indicating radio beacon, which is often called an "EPIRB rescue beacon."
Sometimes, the speaker of a RAS Syndrome phrase is unaware that he or she is using a verbal redundancy to describe something, because he or she might not know the words that the acronym represents. Although RAS Syndrome redundancies would sound wrong when they are spelled out in their entirety, many of them sound right when they are in acronym form. The redundancies might be present to make the acronym more representative of the description, because few acronyms make it obvious what they represent.
RAS Syndrome describes only some of the verbal redundancies present in the English language. Rhetorical tautologies, for example, use two words in a sentence to say the same thing. Some examples are "safe haven," because a haven intrinsically implies safety, or "previous experience," because experience, by definition, is in the past.