GT"--Grand Tourismo.. grand touring.,,,,,, type of model intented for touring needs rather than general use but is ofcourse can be used for regular use.
i"-- mostly abbreviated for injection,,,,fuel injection type engine
Gt ti"- again touring car with turbo tuned fuel injection engine.
touring cars tend to have better road handling features from advanced suspension /braking etc.
touring can be but need not to be luxury models in terms of powered features like power windows etc.... again depends on manufacturer