Similar to the wired Wake-On-LAN, WWOL allows the system to suspend (ACPI S3) or enter another low-power state while keeping the wireless interface(s) active. Events like receiving a user-specified pattern of packets, a magic packet frame, or being disconnected from an access point can then trigger the system to return to its default state. This could also be used for automatically resuming the system when the wireless network adapter locates a suitable WiFi network to connect.
This support comes via patches that were originally published back in May (on linux-wireless) and during the Linux 3.1 merge window they finally worked their way into the mainline tree.
Intel added WoWLAN support to their iwlagn driver via this commit.
This wireless network feature is on top of a number of other features to be introduced in the Linux 3.1 kernel when released next month.