A kilometer is a unit of length or distance. It's defined as
the length of 1,000 meters.
To perhaps give you a better feel for it . . .
1 kilometer = about 1,094 yards
1 kilometer = about 0.621 mile
1 mile = about 1.61 kilometers
Almost every place in the world outside of the USA posts their
distances and speed limits on their road signs in kilometers
instead of miles.