A set of leading digits dialed before the local subscriber number. In telephony routing, prefixes identify country codes, area codes, or central office codes to direct the call through the public switched telephone network. They also designate special billing arrangements like toll-free or premium-rate services.
Heard on the job
We need to block that entire 900 prefix at the PBX level so nobody racks up premium charges.
Insider tip
In the North American Numbering Plan, the central office code (the first three digits of a seven-digit local number) is often specifically called the prefix.