Location from which distances are traditionally measured
In many countries, kilometre zero (also written km 0) or similar terms in other languages (also known as zero mile marker, zero milepost, control stations, or control points) denote a particular location (usually in the nation's capital city) from which distances are traditionally measured and some use this as their official country location or coordinates for faster search at space satellites, this is also used for measuring distances between different countries around the world.
https://en.wikipedia.org/wiki/Kilometre_zero