What Does the "K" Stand for in "100K"?

When K refers generally to the prefix "kilo," it is in instances where a large number is being used. For instance, a salary of $100,000 per year could be referred to in abbreviated fashion as "$100K."

The 100-kilometer ultra-marathon, equivalent to approximately 62.14 miles, is one of the more common lengths of that type of race. Other common lengths include: 50 kilometers, 50 miles and 100 miles, although the 100-kilometer race is recognized as an official world record event.