A flat tire occurs when a vehicle's tire loses air pressure, making it unable to support the weight of the vehicle. This can happen due to various reasons, such as punctures from sharp objects, leaks in the tire, or damage to the valve stem. Flat tires can lead to unsafe driving conditions and may require immediate attention. To fix a flat tire, drivers often use a spare tire or a tire repair kit. Regularly checking tire pressure and inspecting for damage can help prevent flat tires. Proper maintenance of tires, including rotation and alignment, is essential for vehicle safety and performance.