Here are some common terms that can be useful as you explore Internet telephony. These terms are adapted from the Dialogic Internet Telephony Glossary
Computer telephony (CT): Where a computer is an integrated part of the outgoing/reception and management of telephone calls.
Gateway: The entrance way to a communications network. Technically speaking, this device intercepts and steers electrical signals from one network to another.
H.323: An adopted standard for the Internet telephony community to communicate over any packet network, including the Internet.
Internet protocol (IP): Referring to a 32-bit number for a specific TCP/IP host on the Internet -- describing software that tracks the Internet address of nodes, routes outgoing messages and recognizes incoming messages.
Internet service provider (ISP): A company that provides users with a connection to the Internet.
Internet telephony: The technology that allows voice phone calls to be made over the Internet or through a packet network using a PC, a standard phone or a gateway.
Private branch exchange (PBX): This is the equipment owned by a company that routes all incoming and outgoing phone calls.
Voice over Internet protocol (VoIP): Building on and complementing existing standards such as H.323, this directive for developing and promoting standards for Internet telephony was established in 1996 by Cisco Systems, Microsoft Corp., Dialogic, U.S. Robotics Corp. and VocalTec, among others.