What is meant by the term 'off-tracking' in a commercial vehicle?

Off-tracking is the natural geometric tendency of the rear wheels of a tractor-trailer to follow a tighter path through a turn than the front wheels. The longer the wheelbase, the more pronounced the off-track. This is why a tractor-trailer making a right turn must swing wide to the left before turning, to give the trailer's rear wheels room to clear the curb on the inside of the turn. Failing to swing wide enough causes the trailer's rear wheels to climb the curb or run over a pedestrian or vehicle in the right turn lane. New drivers often turn too sharply because they steer like a car. Always plan the turn so that the trailer ends up in the correct lane, even if the tractor has to take an unusual line to get there.