History
The phrase "Triple Crown" was originally applied in Great Britain to an English, Irish, Scottish, or Welsh national Rugby team that defeated all three of its opponents in a single season.
It was next used for England's three major horse races, the Two Thousand Guineas, the Derby, and the St. Leger. When Gallant Fox won the Kentucky Derby, Preakness, and Belmont in 1930, sportswriter Charles Hatton brought the phrase into American usage.
It has since been adopted by baseball and by harness racing, which has two Triple Crowns, one for trotters and one for pacers.
This probably isn't startling news, but it always refers to winning three of something.
Horse Racing
The Triple Crown events in Thoroughbred racing are the Kentucky Derby (first Saturday of May), the Preakness Stakes (third Saturday of May), and the Belmont Stakes (2nd Saturday of June).
Long an imaginary title, the Triple Crown was given official status in 1987, when the three tracks created the Triple Crown Challenge, with a $5 million bonus to any horse that won the Triple Crown. If no horse won all three races, a $1 million bonus was awarded to the horse with the best overall record. The challenge was discontinued after 1993.
Twenty-five three-year-olds have won the first two races in the the Triple Crown but only eleven of them have gone on to win the Belmont. They're listed below, with their jockeys and trainers.