Also know as Ethernet or data extensions. You may need Ethernet extensions for those places where wireless (WIFI) does not give good performance due to distance/interference or you simply prefer to be hard wired. Related information.
Powerline adapters can provide networking through the electric power sockets but a physical wire (Cat5e standard or above) will always provide the fastest and most stable connection possible.
Note that the latest Televisions now often have a Ethernet port on the back to give more T.V. and internet services on the “big screen”, and of course Xboxes, and Playstations will benefit from a solid connection.