PoE, or Power Over Ethernet, is a way to provide electrical power to your wall or ceiling mounted access points using only the network cable.  This way there’s no need to worry about where to plug it in.

The PoE connects to your internet gateway/router (using the LAN socket) and also to the power source.  The Access Point connects directly (using the PoE socket)

Multiple APs

When using multiple APs, you don’t need to purchase many PoE injectors.  Instead you would typically install a PoE switch which behaves in a similar way to an injector, but can provide network and power connections to multiple APs.

A UniFi ToughSwitch

The UniFi ToughSwitch, for example, powers up to 5 devices on a single power source, making venue cabling far simpler, especially for ceiling-mounted access points or other awkward locations.

TIP:  Always use vendor-specific PoE switches.  If for example you connect 3 UniFi AP AC Lite units to a D-Link PoE, sometimes there’s only enough power to run one of them at a time!