Road running is the sport of running on a measured course on road, on either flat or moderately hilly courses. These events would be classified as long distance according to athletics terminology, with distances typically ranging from 5 kilometres to 42.2 kilometres in the marathon. They may involve large numbers of runners or wheelchair entrants.
Trail running is a variant on running that differs markedly from road running and track running. Trail running generally takes place on hiking trails, most commonly single track trails, although fire roads are not uncommon. A distinguishing characteristic of the trails is that they are often inaccessible by road except at the trail heads. The trails tend to traverse varying terrain; hills, mountains, deserts, forests, and narrow passages are common. Likewise, steep inclines or rough terrain sometimes may require hiking or scrambling. Runners participating in trail runs must often descend these same steep grades. It is not unusual for trail runs to ascend and descend thousands of feet.
An ultramarathon (also called ultra distance) is any sporting event involving running longer than the traditional marathon length of 42.2 kilometres (26.2 miles).
There are two types of ultramarathon events: those that cover a specified distance, and events that take place during specified time (with the winner covering the most distance in that time). The most common distances are 50 kilometres (31.069 mi), 100 kilometres (62.137 mi), 50 miles (80.467 km) and 100 miles (160.934 km), although many races have other distances. Other distances/times include double marathons, 24-hour races, and multiday races of 1000 miles or even longer.