Why "PIN Number" is Wrong, Right and Avoidable Anyway
Many people dislike expressions like ATM machine, PIN number and LCD display, where there is an apparent repetition of the last word of the acronym. ATM means "Automatic Teller Machine", they argue, so it makes no sense to say "Automatic Teller Machine Machine". This view is very common; you find it in the Wikipedia page for PIN and in many respectable writing guides like DailyWritingTips . Actually in a way they are all wrong. Somebody who writes "PIN number" is not writing "Personal Identification Number Number", they are writing "PIN number". Through their use acronyms acquire an identity of their own that replaces the original meaning, usually to the point where few people know what they once stood for. LCD was perhaps originally an acronym for Liquid Crystal Display but now "LCD" has just become descriptive of a type of display, like OLED, plasma or TFT. You should, argue the language mavens, just say ATM, PIN