The Ethernet interface is a cable bus which runs over copper or fiber.
However only the copper interfaces which use differential twisted pairs, use Power Over Ethernet [POE]. This page describes the POE interface.
The 'normal' Ethernet network is defined by IEEE 802.3. A description of the 802.3 interface is found on the main Ethernet page.
POE uses the spare wires not used by the Ethernet interface to deliver a DC voltage over the cable....