To keep your writing as clear and concise as possible, you should generally try to remove unnecessary words. Sometimes duplication is fine – for artistic effect, for example – but as a general rule, it’s best to say things in as few words as possible.
Unnecessary words often creep in when using acronyms. Acronyms are words formed from the initial letters of phrases, as discussed in a previous Daily Writing Tips article. Examples include “laser” (from “light amplification by the stimulated emission of radiation” and “scuba” (from “self-contained underwater breathing apparatus”). But a mistake that is often made is to repeat, unnecessarily, the last word of the original phrase.
An example of this is “PIN number”. In this phrase, PIN is (most commonly) an acronym for “personal identification number”. Written out in full, “PIN number” amounts to “personal identification number number”. This might make sense – if, for example, you were discussing the number of PINs you have – but most likely it’s just nonsense. “Please enter your PIN” makes perfect sense.
There are numerous other examples to be found : ATM machine, HIV virus, ISBN number, LCD display, SAT test and so forth. These are very common mistakes : search for any of them on the internet and you’ll find countless examples. Because they are so common, it’s all too easy to find yourself employing them without noticing.