A **skid or slide** occurs when a vehicle's wheels **lose traction** with the pavement. This means that the tires do not grip the road well, which can cause the vehicle to slide and lose control.

- **Common causes of skidding**: Driving at high speed, making sharp turns, braking suddenly, having tires or shock absorbers in poor condition, or poor load distribution in the vehicle.

- **Skidding in curves**: It is common for skids to occur in curves due to the force pushing the vehicle outward, which can cause the tires to lose contact with the road.

- **Aquaplaning**: A specific type of skid that happens when there is water on the road. The tire cannot evacuate all the water, causing the vehicle to lose control. This is more likely at high speeds or with worn tires.

In summary, a skid occurs when the wheels do not have enough traction, which can be caused by various factors, including road and vehicle conditions.