A kilometer is a unit of measurement used to express distance. It is part of the metric system, which is widely used around the world. One kilometer is equal to 1,000 meters, making it a convenient way to measure longer distances, such as those between cities or landmarks. Kilometers are commonly used in many countries for road signs and maps. For example, a road sign might indicate that a city is 50 kilometers away. This unit helps people understand how far they need to travel, whether by car, bicycle, or on foot.