prefix
[In telephone communications,] an indicator consisting of one or more digits, that allows the selection of different types of number formats (e.g., local, national or international), transit networks and/or the service.
Note 1: Prefixes are not part of the number and are not signaled over internetwork and international boundaries.
Note 2: When prefixes are used, they are always entered by the user or by automatic calling equipment. [T
1. Rpt30-1994]