VoIP uses your dial-up or broadband connection to make free calls over the internet. The acronym VoIP stands for Voice over Internet Protocol and is the technology for transmitting voice conversations via the internet - it's what's under Skype's bonnet if you will.
VoIP has been called a few different things in its colourful past such as internet telephony, peer-to-peer, P2P, IP telephony, broadband telephony, voice over broadband and many, many other names. At Skype we much prefer using the simpler term free calls over the internet than the geeky VoIP.
VoIP solutions are available both for individual and business users - both offer great ways to save money compared to the call charges of many phone companies and calling cards. Skype also offers a business VoIP solution called oddly enough Skype for Business.