Wide Outside Lane... meaning the rightmost lane (US) and the width of that lane, which is often wider than any other adjacent lanes.
Wider than any other adjacent lanes is not what determines whether a lane is "wide". What determines whether a lane is "wide" is whether it is wide enough for a bike and motor vehicle to safely share side-by-side. Most sources agree that that means the lane has to be at least 14 feet wide, some say 15 feet. If such a lane is the outside lane, then it's a WOL.
Note that a typical 12 foot lane plus a narrow 4 foot bike lane is 16 feet wide.