The art of using a laptop computer and specialized "sniffing" software to located usable 802.11 wireless networks--while driving. See also "war chalking."

The sport of the uber leet. You scan for wi-fi networks on your laptop whilst driving around, sitting in mall parking lots, outside the hot chick you have your eye on's house, etc.

Some popular programs war drivers use are:
Netstumbler: http://www.netstumbler.org
Wardrive ToolBox: http://www.xenon-inc.com
Ethereal: http://www.ethereal.com
Aircrack: http://freshmeat.net/projects/aircrack

Just remember, it may be illegal to use a wireless access point without permission from the owner.

war driving = Drive around in a car, searching for wifi networks, and hack them!

Tools:
Net Stumbler
Air Snort

owening people's networks by "netstumbling" their wifi.