There is not actually a firm consensus and it can depend on your region where the term appears.
Gran Turismo Injected
Grand Touring Injected
Grand Touring International
The idea is of a practical sized car that is build for lots of long fun journeys a tourer, that is grand or of a high specification.
As most cars are now injected anyway the i seems pointless but it did make these new fuel injection models stand out from the Carb fed crowd of it's day.
It was primarily associated with the VW Golf, the definitive hot hatch for many people.
Many marques just use GT today to convey the thought of a practical sporty car.