To have a tendency to want or to be interested in mechanical things; to understand, and be able to work on things of a mechanical nature, or things with gears.
A person who is into all things motorized. This can be cars, motorcycles, machines, planes, or boats, but specifically relating to the engine and power delivery. Knowing how to weld and machine metal are also traits of a gearhead.
Dude, she's such a gearhead. Go show her that old lathe and tools in your grandfather's garage and she'll be in heaven.
Person who in a MMO group will check teammates gear and then express his disgust for those who dont have equipped the best of the best regardless of current challenge level.
Person one:"OMG! Why u using that gear?! Get sumthin better! Heirlooms!"