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 a puncture from a sharp object, a slow leak, or damage to the tire itself. Driving on a flat tire can cause further damage to the tire and the vehicle's wheel. To fix a flat tire, drivers typically need to replace it with a spare tire or repair it using a patch or sealant. It's important to regularly check tire pressure and condition to prevent flats. Tools like a tire pressure gauge and a jack are often used in the repair process.