In short, the ability for a computer to
boot itself up when it detects
network traffic.
If you have a
PC with an
ATX mainboard, chances are it has a Wake-On-
LAN connector. If your
NIC also supports WOL (I haven't been able to find many that
don't), then hook the two connectors together with a WOL cable. Get the
MAC address of the system you're turning off and then
soft power-down the system -- if the
"link" light on the
hub/
switch goes out when the power does, WOL isn't going to work on this system. To wake up the system, use a program on a different host that can generate "APIC Magic Packets" and have it send one to the appropriate MAC address. The system should turn itself on and boot up.
On PC's, this works only for ATX mainboards (because on
AT's, when the power's off the mainboard doesn't have power). I don't know if non-PC systems have support for similar features.