10K is a long distance running event. It is run in the Olympics as well as a road race that is popular among recreational runners.
The 10,000 metres or 10K is a common long distance running event. As '10,000 metres' it is a track event, and appears in athletics events such as the Olympic Games and the World Championships in Athletics; as '10K' it is a roadrace or cross country running event. The 10K road race is a popular distance among recreational runners.
Contributions by Montell 74, CutOffTies, and Canada Jack.