A powerline network is a way to use a building's existing electrical wiring to bridge multiple segments of a local area network. Using one is a simple way to create new wired network connections without the hassle of running new Ethernet cables.
Powerline networks extend a home network to places Wi-Fi struggles to reach. A brick wall can interfere with a Wi-Fi signal, but creating a powerline network that runs from one side of the wall to the other gets around that interference. Powerline networks are slower than Ethernet and MoCA networks but can provide a stable network extension when those options are unavailable.
Using a powerline network involves using two or more powerline adapters. First, plug one adapter into a standard electrical wall outlet and connect it by Ethernet to a router. Plug another adapter into a wall outlet in an area that needs a network connection, then use the adapter's Ethernet port to connect a device, like a computer, wireless access point, or network switch. The adapters will then bridge the networks using the electrical wiring in the walls.
NOTE: Powerline networks have some significant limitations that are important to know. Speeds claimed by adapter manufacturers only apply to ideal conditions, which are unlikely to exist in real-world use. The quality and layout of the electrical wiring have an impact, and speeds will be faster between two adapters on the same circuit than between two adapters on different ones. Appliances that draw significant power, like a dryer, can cause interference while running.