Voice over IP (also called VoIP, IP Telephony, Internet telephony, and Digital Phone) is the routing of voice conversations over the Internet or any other IP-based network. The voice data flows over a general-purpose packet-switched network, instead of traditional dedicated, circuit-switched voice transmission lines.

Protocols used to carry voice signals over the IP network are commonly referred to as Voice over IP or VoIP protocols.

Voice over IP traffic may be deployed on any IP network, including ones lacking a connection to the rest of the Internet, for instance on a private building-wide LAN.

[source: Wikipedia.org]