Voice over Internet Protocol (VoIP), also known as IP telephony, refers to a set of technologies used for voice communication sessions over Internet Protocol networks, such as the Internet.
Moreover, it is a communications technology that enables you to make phone calls using your broadband connection instead of landline service.
A typical setup involves a router for the internet with a handset connected. The handset or business phone system uses the internet to transmit your speech like a physical landline would. The only difference is that the underlying technology is not a landline but the Internet.