GTI stands for "grand tourer--injected" or "grand touring--injected", a designation typically reserved for sporty coupes. Although initially a technical classification, current carmakers use the acronym as a performance-oriented marketing tool.
The first car to be marketed with the abbreviation "GTI" was Maserati's 1961 3500 model. This car introduced fuel injection to the grand tourer class, hence the addition of an "I". Since then, GTI has become associated with performance.
GTI belongs to a whole group of grand touring classes, including GTO, GTR and GTA. These cars all claim high performance, comfort and luxury as defining traits, hence "grand touring"--they're supposed to be ideal for long-distance trips.
GTI's are among the smaller of the GT types, with most being coupes and hatchbacks. A typical example is the Volkswagen Golf, which began production in 1976 and remains popular to this day. Most GTI's are two-door models, though four-door examples exist.
None of the GT labels, including GTI, have any official standing beyond car-enthusiast circles. The close association they have with a sporty image has made them popular with manufacturers, but there are no actual standards for this practice.
In the 1960's when fuel injected cars were still a distinct minority, the GTI label offered novelty value. With all new cars having fuel injection, the moniker has become useful only for its promotional value.
"Grand touring", or "grand tourer", are the English versions of "gran turismo"--the original Italian term for this type of car.
