A mass start usually refers to an open water swim start or triathlon swim start where all athletes start their swim at the very same time. In most cases, a mass start is either a beach start or an in-water start. Mass starts typically do not have a timing mat at the beginning of the race, as all athletes have the very same event start time, usually referred to as the gun time.
While running mass starts are not uncommon in cross country and on the track in the longer distances (5K, 10K and Marathon), they are generally not talked about as mass starts. Most cycling events, especially larger Gran Fondos and professional stage races, utilize mass starts as well. Each cyclist starts at the very same time, and the first finisher wins.
