These are the general terms for the trucking industry.
The different paths that the front and rear wheels take when cornering. The rear or trailer wheels will take a shorter path around the curve, corner or turn. Thus the driver has to compensate for this shortcoming by taking the curve, corner or turn wider.
Off-tracking is when the rear tires follow a different, shorter path than the front tires. The longer the vehicle the more off-tracking for which a driver must compensate.