Checkers AC Ultra

UltraRunning is devoted to covering the sport of long distance running, also known as ultramarathoning, or, as we prefer, ultrarunning.
How far is 'a long distance'? The standard definition is anything past the marathon, or 26.2 miles.
However, the shortest standard distance that is considered an ultra is the 50 kilometer distance, or 31.07 miles.
Other standard distances are the 50 mile, 100 mile, 100 km, and a series of events that last for specified time periods such as 6 hour, 12 hour, 24 hour, 48 hour, and 6 days (Ultrarunning magazine, 2013).

ultrarunning.com