- The code which identifies a central office. In the NPA-NXX-XXXX ten-digit telephone number format, it is the NXX portion, where N can be any digit between 2 and 9, and X can be any digit between 0 and 9. A single central office may serve more than one prefix. Also called central office prefix, central office code, or NXX code.
- A word element which is affixed to the front of a word to produce a form with a different or derived meaning. For example, the tera- portion of terabyte.
- A letter, number, symbol, or the like, placed before something else. For instance, the Q in Q15.
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