VoIP stands for Voice over Internet Protocol. It is a technology that enables the transmission of voice over an existing IP network (either internet or intranet). VOIP is a way of converting the analog signal when using a phone to digital format (across the network) and then back to analog signal at receiving end.
VoIP is a technology that allows you to make voice calls using a broadband Internet connection instead of a regular (or analog) phone line. Some VoIP services may only allow you to call other people using the same service, but others may allow you to call anyone who has a telephone number including local, long distance, mobile, and international numbers. Some VoIP services only work over your computer or a special VoIP phone; other services allow you to use a traditional phone.