The VoIP definition or synonym is Voice over Internet Protocol and sometimes it's also called an IPT short for IP Telephony. You can pronounce it as V O Y P. VoIP is a telecommunication technology that enables you to make and receive phone calls via the Internet.
You may come across the following terms that are commonly used by many people:
All the above mean the same; however, technical speaking there is a slight difference between VoIP and IPT terminologies (refer to VoIP vs IP Telephony). So no need to get confuse yourself. Leave the technical part to the engineers and scientists.
You may be interested in the following related links:
External related link/s and resource/s:
VoIP Definition - By 3CX
VoIP Features Definitions and Glossary - The Digest
What is Voice Over IP - Mitel