Here is a place to find the background information on what is exactly an ultra-distance racing, what sports have such long distance events, and why anyone would want to participate in such athletic events. Very basic and short answers are below. You can also find additional, and more comprehensive, information at the following Endurance World pages:
"Despite what seems like the extraordinary nature of these events, in the end, they make you even more human." Joel McNamara
Webster's Dictionary definition:
ultra \ adj : going beyond others or beyond due limits : extreme, fanatical, uncompromising, superlative
1: beyond in space : on the other side
2: beyond the range of limits of : transcending
3: beyond what is common, ordinary, natural, right, proper, or moderate : excessively : exceedingly
Ultra-distance athletic event is traditionally any race over the standard long-distance "peg" typical for this specific sport (i.e., over marathon distance in running). But ultra event cannot be purely defined by the distance criteria. There are certain shorter events that also may be considered ultra due to terrain, weather, and other conditions that greatly increase difficulty and finishing factor. Multisport stage events and multi-day adventure races would also fall under the definition of an ultras. Certain "solo" undertakings by individuals and/or uncommon athletic achievements also deserve an ultra status. Ultra distances can be raced in a variety of sports, from ordinary (as running, cycling, and swimming) to more exoteric (as triathlons, skating, sailing, paddling, climbing, equestrian and others).
Some athletes that prefer ultra-distance to shorter races do so because of the intensity such events generate. In ultra races, there is also a tremendous sense of accomplishment in just finishing. Winning is not the only goal, as is often the case in shorter races. Extreme distance races are also process rather than goal-oriented; athletes usually undergo unique experiences of failures and traumas of some sort before crossing the finish line. How an athlete reacts to the process will dictate his or her success. It is this particular aspect of ultra racing that some athletes relish most. To prepare, many athletes find it impossible to log anywhere near the number of miles they cover in the race itself, so they do not even try. Since most ultra-distance athletes already possess (and feel confident about) their base fitness, they prefer to work on specifics in their training (targeting weaknesses) or on general fitness maintenance. Besides training and fitness preparations, the importance of staying well-fueled during races is another main concern, as lack of proper nutrition is the most common reason for DNF.
There are certain truths and commandments that applicable to any long distance racing event. They are preached by many seasoned athletes but sometimes new athletes need to be learned by their own example to believe. Below is a compilation of some of such advices.
Never try anything in the race that you have not tried first in training. Test you body, your gear, your nutrition during training first.
You don't need to cover race distance mileage in your training. Usually, one (progressively) long session per week and consistent training will be adequate.
You don't need to always train at race pace in your training. Variety of speeds, efforts, terrain will help keeping training fun and keep overtraining and injuries away.
Train for the race (prepare for terrain, weather and other conditionsexpected in the race).
Nutrition, hydration, and electrolytes can not get you to the finish line but they surely can stop you from getting there.
Ultra-distance triathlon event is typically any race over the standard ironman distance (2.4 mile swim, 112 mile bike, and 26.2 mile run). Triathlon ultras can be be held in a continuous or stage formats. In stage races, participants rest between the segments of the event, with their finishing times for each segment added for the total finishing race time.
An ultramarathon is any footrace beyond the standard marathon running distance of 42 kilometres, 195 metres (or 26 miles, 385 yards). Ultra distance running races typically begin at 50 kilometers and can extend to practical infinity. The longest certified ultramarathon in the world is The Ultimate Ultra, Sri Chinmoy 1,300 Miler (2,092 kilometers). There is also Trans America Footrace, which is run in 64 consecutive daily stages from Los Angeles to New York (almost 3,000 miles total, with about 45 miles (72 km) per day.
Ultramarathons are held on roads, trails and running tracks. They can be point-to-point, out-and-back, or on loop courses. Athletes in ultramarathons "go as you please" (they may take walking breaks, rest to eat, and even sleep without penalty, except for the time or distance a runner loses). Ultramarathons can be of two types: those in which a fixed distance must be completed (50 km, 50 miles, 100 km, 150 km, 100 miles, 200km, 200 miles, 1,000 km and 1,000 miles), and those in which the longest possible distance within a fixed period of time must be covered (12 hours, 24 hours, 48 hours, 6 days). Additional examples of ultrarunning include journey running (trans-country and trans-continent) and mega-running (accummulation of succesful finishes in ultramarathons).
An ultra distance cycling race is any organized event beyond the usual and customary long distace bike race. This is a fluid definition since race course terrain, environmental conditions and duration are three elements that define cycling ultra. Traditional events include 24 hour and transcontinental races.