A Presta valve is a type of valve commonly used on bicycle tires. It is narrower than the more common Schrader valve and features a threaded stem with a small locking nut. This design allows for higher pressure inflation, making it ideal for road bikes and performance cycling. To inflate a tire with a Presta valve, you first need to unscrew the locking nut and press down on the valve to release a small amount of air. Then, you can attach a compatible pump, such as a floor pump or hand pump, to fill the tire with air.