Voice over Internet Protocol (VoIP) is also called IP telephony. It uses a set of technologies to deliver voice communications over internet protocol (IP) networks such as the Internet. In other words, VoIP is a technology that allows people to make voice calls over the Internet. WhatsApp, Facebook, and Skype calling feature are some ideal examples. To make a traditional voice call, you need a phone system connected to a cable line while VoIP only requires the Internet connection to connect people on calls. Voice is very cost-effective for all type of businesses because they have to pay only for the Internet usage.
Source: https://busict.com.au/blog/things-you-should-know-before-switching-to-a-voip-system/