Definition of a touring car

[mtpanorama]

Hey everyone, i dont usually come into this forum, but i was hpoing that someone with a technical memory maybe able to help me (and a few others) with the defintion of a touring car.
A Touring Car from my understanding is a vehicle with a minimum of 4 seats which complies with a specific set of internal dimensions to accomodate passengers. I would assume the majority of 4 door vehicles would be classified as Touring Cars.
I am looking for the exact formula to work this out or to a link for any info on working this out.
The reason i am looking for it is "touring cars" are allowed in our race series (improvrd production in Australia), but no one knows the exact definition of one. Some people are interested in running cars that are 2 door coupe's and are wondering if they fit the "touring car" formula.

Thanks Shane