Although it is applied to a class of automobiles today, it predates the automobile by a considerable amount of time. In England, as far back as the 17th Century, Peers of the Realm and members of wealthy families would go on long trips to travel the European continent. The journey was called the "Grand Tour", and it was an expected part of a young gentleman's education. The Grand Tour could last for several years, and was made by horse-drawn coach. Major continental cities, including Paris, and historic landmarks were stops on the route. The very final destination was always Rome, the center for European art and culture since the Renaissance. There, participants would socialize with their peers and scholars, and enroll in courses of academic study to pursue a classic education. The carriages used for the Grand Tour acquired the name "Gran Turismo" in Italian. When automobiles replaced horse-drawn carriages as the conveyance of choice for a certain type became popular. It was a fast and light two-seater, but more comfortable and well appointed than a pure sports car. The genre reached it's peak after World War 2, when limited-production and specially-constructed two-seaters became popular with members of royalty, wealthy sportsmen, and movie stars. Many of these cars were raced, and the production car category in European racing became known as Gran Turismo, Grand Touring, or just plain GT. Regulations required two-seat interiors, spare tires, and luggage capacity, and, in the 1950s at least, GT-class racers could be and were driven to the track, raced, and driven home. Production-based racing classes are still know as "GT" classes in many racing series today.
But I think Jordan answered your question already, didn't he? 
