power line networking
Power line networking uses power line communications (PLC) to connect computers using existing power outlets in the home, essentially transforming every electrical outlet in the building into a network connection. Power line networking is one of the cheapest forms of home networking and has a low start-up cost and minimal IT workload. And despite using power outlets it also will not have an adverse effect on home electric bills. Power line networks can transmit phone calls and faxes as well as Internet services over regular electrical wiring.
See also power line communications (PLC).