Power over Ethernet (POE) is a technology that lets network cables carry electrical power.
For example, a digital security camera normally requires two connections to be made when it is installed:
A network connection, in order to be able to communicate with video recording and display equipment
A power connection, to deliver the electrical power the camera needs to operate
However, if the camera is POE-enabled, only the network connection needs to be made, as it will receive its electrical power from this cable as well.