A kilometer (km) is a unit of length in the metric system, equal to 1,000 meters. It is commonly used to measure distances between geographical locations, such as cities or landmarks. The metric system is widely adopted around the world, making kilometers a standard unit for road signs and maps in many countries. Kilometers are often used in various fields, including science, engineering, and transportation. For example, automobiles typically display speed in kilometers per hour (km/h), while athletic events like marathons are measured in kilometers to indicate race distances.