A kilometre is a unit of measurement used to quantify distance. It is part of the metric system and is equal to 1,000 metres. The symbol for kilometre is km. This unit is commonly used in many countries around the world for measuring longer distances, such as the distance between cities or the length of a marathon. Kilometres are often used in road signs to indicate how far one location is from another. For example, a sign might show that a city is 50 km away. This makes it easier for people to understand distances when traveling or planning trips.