NXX code

1. In the North American direct distance dialing numbering plan, a central office code of three digits that designates a particular central office or a given 10,000-line unit of subscriber lines; “N” is any number from 2 to 9, and “X” is any number from 0 to 9. 2. The three digits (in positions 4, 5, and 6) in an YYY-NXX-XXXX number.