Track is a measurement of wheel placement, similar to wheelbase but rather than measuring the distance between front and rear axles, track is a measurement of the distance between the two outermost points of contact between a vehicle and the ground.

For most of us this means the outer edge of the contact patch on the two rear tyres on your car.

Two wheeled vehicles like motorcycles do not have a 'track' measurement as such, but if they did it would be the width of the contact patch of a single tyre.

As with wheelbase, more track provides greater stability at the expense of turn-in ability.

The simplest way to increase the track of a vehicle is to fit wider tyres, but only a small increase can be made without changing wheels.

Other methods include fitting wheel spacers (unsafe) or to fit wheels with a different offset to standard (also unsafe, but much better than using spacers).

All of the above can cause problems with clearance between your tyres/wheels and the vehicle's wheel wells, which would in turn make the vehicle unsafe.