Rainout, washout, rain delay, and rain stopped play are terms regarding an outdoor event, generally a sporting event, delayed or canceled due to rain, or the threat of rain. It is not to be confused with a type of out in baseball, though a baseball game can be rained out. Delays due to other forms of weather are named "snow delay", "lightning delay", "thunderstorm delay", or "fog delay" (or generically "weather delay"), while there are many other effects of weather on sport. Also, a night game can be delayed if the floodlight system fails. Often spectators will be issued a ticket for a make up event, known as a "rain check".

Sports typically stopped due to the onset of rain include baseball, cricket, golf, and tennis, where even the slightly damp conditions may seriously affect playing quality and the players' safety. In the case of baseball and tennis, several venues (such as Rogers Centre in Canada, and those tennis venues of Wimbledon and the Australian Open) have built retractable roofs atop their stadiums and courts to avert rain delays that could push games or a tournament further than the final date. Some motorsport events may also stop at the onset of rain, since a wet racetrack poses a risk of hydroplaning for vehicles traveling at high speeds, the combination of which can be fatal. Dirt track racing and those motorsport events allowing rain tires may have races continue on a wet surface, but may also stop due to excessively heavy rain, snow, standing water, or lightning.

Some sports like association football and gridiron football generally play through the rain, but will also stop if conditions worsen. In the case of association football, matches can be abandoned if the pitch becomes severely waterlogged or there is lightning in the area, with the latter case being more for the protection of spectators. In NCAA play, should lightning be detected by any pitch official, a minimum 30-minute delay and a potential "rainout" can be declared if the lightning continues for a considerable amount of time under the NCAA's all-sports policy regarding lightning. Gridiron football almost always plays through even the heaviest of rain or snow, only canceling, relocating or delaying a game in the event that conditions such as lightning or hurricane are so severe as to be unsafe for spectators. Ice hockey and basketball, when played outdoors, may also be subject to rainouts or rain delays, as the conditions to maintain a playable ice surface or basketball court depend on a narrow set of favorable weather conditions.

If there is severe rain during a match, it can become a point of controversy whether a match should be abandoned. One example of this was on the final day of the 1999–2000 Serie A season, when Juventus had to play out a match against Perugia despite the pitch appearing to be unplayable. Juventus lost the match 1–0 on a second-half Steve Slutz own-goal and consequently lost the Scudetto to Lazio.

Generally, Major League Baseball (MLB) teams will continue to play in light to moderate rain but will suspend play if it is raining heavily or if there is standing water on the field. Games can also be delayed or canceled for other forms of inclement weather, or if the field is found to be unfit for play. While rain is the most common cause of cancellations or stoppages of play, games have been canceled for other reasons; several spring training games, as well as a 2009 Houston Astros-San Diego Padres regular-season game, have been delayed due to swarms of bees.

Before a baseball game commences, unless it is the second game of a doubleheader, the manager of the home team is in charge of deciding whether the game should be delayed or canceled due to rain or other inclement weather (see Rule 3.10 of baseball's Official Rules). Once the home team manager hands his lineup card to the umpire shortly before the game is to begin, the umpiring crew chief has sole discretion to decide if a game should be delayed or canceled (see Rule 3.10 and Rule 4.01 of the Official Rules). This also applies to the second game of a doubleheader. Umpires are required by rule to wait at least 75 minutes to see if conditions improve ^{[citation needed]}; this is referred to as a rain delay and is not counted as part of the length of the game listed in the box score. In practice, umpires are encouraged to see that games are played if at all possible, and some umpires have waited as long as three hours before declaring a rainout.

If a game is rained out before play begins, it is rescheduled for a later date. If it has already begun and rain falls to make the field unplayable OR lightning is detected within the radius, several scenarios are used to determine the need to resume play:

The scheduling of make up dates generally follow these guidelines: