Sprints are races in athletics. They are roughly classified as events in which top runners will not have to "pace themselves", but can run as fast as possible for the entire distance. These are often the more glamorous events in Olympic Athletics.

Common distances

60 m
The 60 metres is normally run indoors, on a section inside an indoor athletic track (which is only 200 m long). As the races last between six and seven seconds, having good reflexes and thus getting off to a quick start is more vital in this race than any other. 
This is roughly the distance required for a human to reach maximum speed and can be run without breathing. It is popular for training and testing in other sports (e.g. speed testing for American football, although 40 yards is more common there). 

100 m
The 100 metres is the best-known sprint distance, and alongside the marathon it is arguably athletics' most prestigious event. It takes place on one length of the home straight of a standard outdoor 400 m track. Often, the world-record holder in this race is considered "the world's fastest man/woman". 
This race distance would be hugely different indoors, as the need to go round a tight bend would slow runners down significantly. Either way, it could be run without breathing. 
The 4 by 100 m relay is another prestigious event, with an average speed that is quicker than the 100 m, as the runners can start moving before they receive the baton. 
World Record progression 100 m men 

200 m
This begins on the curve of a standard track (where the runners are staggered in their starting position, to ensure they all run the same distance), and ends on the homestraight. 

The ability to "run a good bend" is key at this distance, as a well conditioned runner will be able to run 200 metres in an average speed higher than his 100 m speed. 
This race is run indoors, as one lap of the track, with only slightly slower times than outdoors. 
Four-person relays are occasionally run at this event. 
A slightly shorter race (but run on a straight track) was the first recorded event at the Ancient Olympics. 

400 m
400 metres is exactly once around the track on the inside lane, but of course the runners are staggered in their starting position. While this event is a sprint, there is more scope to use tactics in a race - the fact that 400 m times are considerably more than four times 100 m times demonstrate this. 
Relays are commonly held at this event. 

Uncommon distances

150 m
This informal distance can be used to work on a 100 m runner's stamina, or a 200 m runner's speed, and has been used as an exhibition distance. The last famous duel was held between 1996 Olympic Champions Donovan Bailey (Canada) and Michael Johnson (USA). 

300 m
Another informal distance, which could be used to aid a 200 m runner's stamina, or a 400 m runner's speed. 

500 m
More common (or less uncommon) than 300 m and 150 m, because this can be seen as the half-kilometre. This obviously could aid 400 m runners' in their stamina, or help a middle-distance runner to gain speed. 

Sprinters

Versatile Athletes
Most athletes will not be able to compete exclusively in one sprint event. Reasons for this could be pragmatic: only being willing to race over one distance might not earn an athlete enough prize money (or media exposure, which can lead to more money) to survive on. Where this doesn't apply, such as for more high-profile (i.e. rich) runners, an athlete may feel that running over two events is more enjoyable and varied, and gives them a better chance of success.

The indoor season is often not run by certain high-profile athletes, who may not like the atmosphere, different distances or extra corners involved. Again, some will have to run in this season in order to make a living.

While certain athletes will be strictly 100 metre runners, and will run further distances only for fun or money, many will compete in multiple events. Namibian Frankie Fredericks has been successful over 100 m and 200 m (and may run the 60 m and/or 200 m in the indoor season). Michael Johnson won gold medals over 200 m and 400 m in the 1996 Olympics, and also in the 4 x 400 m relay. Runners can do well in relays when they are competitive in the individual event.


Hurdlers
Sometimes 100 m and 400 m runners have competed in the hurdles events at the same distances, and there is a certain amount of interchangeability between the flat and hurdle events, although it is difficult to be a world class competitor in both events. Sometimes runners will start off as a hurdler and then, catalysed by an event such as injury, will switch to flat races. It is more common for hurdlers to go to the flat than for runners to start hurdling.

Often a 400 m hurdler will be able to run the 4 x 400 m relay, Chris Rawlinson of Great Britain being a good example. This is possibly partly because the hurdles and the relay involve a less "controlled" environment, containing obstacles such as opposing teams jostling for position (after 600m of the relay, the runners break lanes, and are allowed to take the inside lane) or the hand-over of the baton, or physical obstacles - the 91 cm/76 cm (men's/women's) hurdles.


Biological factors for runners
Some biological factors that can determine a sprinter's potential are:

Muscular strength (more important than in longer events) 
Adrenaline use 
Anaerobic respiration capacity (not as important as in longer events - some of the shorter sprints can be run without having to breathe at all) 

Other sports
The most common distance for rowing races is 2 kilometres. Races may be held at less than 1km, which are known as sprints. 
Horse Racing has sprint distance events. 
Track cycling features a sprint event, in which usually two riders compete over a distance of 1000 metres, though only the final 200m may be timed. However, the time is normally immaterial - the aim is to be first across the line and win two races in a 'best of three races' match.