The kilometer (km) is a unit of length in the International System of Units (SI). It is defined as exactly 1,000 meters.
The kilometer was first adopted in France in the late 18th century during the French Revolution. The metric system was established in 1795, with the kilometer becoming a standard unit for measuring distance. The term "kilometer" combines the Greek prefix "kilo-" (meaning one thousand) with the meter.
Kilometers are commonly used in everyday life for measuring distances between locations, especially in countries that utilize the metric system. It is widely used in scientific applications, engineering, and transportation. Most countries, except for the United States, use kilometers for road signage and distance calculations.