What is the reason for skidding?

Answer 1

Skidding is the result of loss of traction or excessive friction. If you attempt to suddenly stop a moving object on a slippery surface, the friction from the surface is no longer acting upon the object. Instead, the object is floating over the surface using the slippy substance as friction (which creates little if none).

On the otherhand, objects such as tires can skid when the tire itself is taking the friction instead of the rotor. Essentially the tire is attempting to dig into the road to slow/stop versus the breaks because the breaks are fully applied and typically locked unless ABS activates.

Answer 2

Not enough friction between the tyres and the road surface. This may be due to bald tyres, or a layer of water of the rod (aquaplaning), or low friction materials like oil of ice.