Often, IT personnel prefer to maintain client systems after employees have gone home. Even if these tasks are automated, client machines must be left on. In the past, if they weren't left on, personnel had to manually turn them on. But, with wake-on-LAN, client systems can be remotely and automatically powered up.
Wake-on-LAN technology resides in a PC's managed network adapter and motherboard. The two are attached via a wake-on-LAN cable terminated by a 3-pin connector on each side.
When the system is turned off, the managed network adapter uses an alternate power source to monitor the network and watch for a wake-up packet from the server. Once it receives a packet, it alerts the system to power up and accept any maintenance task it is given.
Wake-on-LAN is a part of Intel's Wired for Management System and is a result of the Intel-IBM Advanced Manageability Alliance.
Wake-on-LAN is also called remote wake-up.