Power over Ethernet (PoE) is technology that passes electrical power over twisted-pair Ethernet cable to powered devices (PD), such as active loudspeakers, in addition to the networked audio data. It enables one RJ45 cable to provide both audio data and power to loudspeakers instead of having a separate cable for each. 
Several PoE standards exist, differing in delivered power: standard PoE IEEE 802.3af (13W, not used in our products); PoE+ IEEE 802.3at (30W), and more powerful standards. At this time, PoE+ is the most widely available and commonly used standard that delivers enough power for common audio applications.