A device that adds power to an Ethernet cable for Power Over Ethernet (PoE) equipment. Although Ethernet switches are available with PoE capability, millions of regular "non-PoE" switches are already installed. See PoE
The injector plugs into an electric outlet and adds power to the Ethernet cable. In this example (bottom), it enabled an access point to be installed on the ceiling of a home without requiring a power outlet nearby.