Power over Ethernet (PoE)

Source

Power over Ethernet or PoE describes any of several standardized or ad-hoc systems which pass electrical power along with data on Ethernet cabling. This allows a single cable to provide both data connection and electrical power to devices such as wireless access points or IP cameras. Unlike standards such as Universal Serial Bus which also power devices over the data cables, PoE allows long cable lengths. Power may be carried on the same conductors as the data, or it may be carried on dedicated conductors in the same cable.

Since only two of the four pairs are needed for 10BASE-T or 100BASE-TX, power may be transmitted on the unused conductors of a cable (see figure above).

Ref. Wikipedia