^^ WRONG!!!!!!
Wheel Offset -- This is in relation to track width, but refers specifically to the wheels of the car. The more offset a pair of wheels has, the wider the track and overall width of the car will be. Most HPI sedan wheels are 0mm offset, meaning the edge of the wheel hub that comes in contact with the axle hex adapter is exactly in the middle of the wheel. Some wheels, for example, feature an offset of 3mm, which widens the car a total of 6mm.
The 4x100mm is refered to as the P.C.D., or Pitch Circle Diameter.