Kilometer per hour (km/h) is a unit of speed that measures how many kilometers are traveled in one hour. It is commonly used to express the speed of vehicles, such as cars, bicycles, and trains. For example, if a car is traveling at 60 km/h, it means the car will cover 60 kilometers in one hour. This unit is part of the metric system, which is used in most countries around the world. In contrast, the mile per hour (mph) is often used in the United States and a few other countries. Understanding km/h is essential for interpreting speed limits and travel times.