NXX

A three-digit code in which N is any digit 2 through 9 and X is any digit 0 through 9. Typically used in describing the "Exchange Code" fields of a North American Numbering Plan telephone number. The full numbering system is in the format of "Area Code" + "Exchange Code" + "Line Number" or NPA-NXX-XXXX. A central office will have one or more area and exchange codes.