It's important to recognise that Powerline and Powerline Communications (PLC) are effectively two different things, although both make use of power cables to deploy an Internet or local network connection.
Powerline Communications (PLC) - This allows the broadband transmission of Internet access along existing national grid power cables and into the home or office. It is another form of Internet access delivery but has been known to cause a lot of interference with other devices (radios etc.) and was not able to keep pace with faster fixed land-line or wireless broadband solutions.
Powerline or HomePlug - These are the names most frequently given to Ethernet (local network adapters) that connect into your home/offices standard power/plug sockets and effectively turn the buildings internal power wires into network cables. This is handy if you don't wish to use a wireless (Wi-Fi) solution and don't fancy trawling a long cable around your building to connect computers - just plug an adapter into the walls power socket and connect.