What is the origin of expression Grand Theft Auto?

Answer 1

Firstly, Auto is simply short for automobile.

Grand Theft is an American term for a felony crime involving the theft of objects worth a certain value - that value can change from state to state. It can vary from $100 to $1000. However this distinction is usually ignored when talking about the theft of an automobile, this is almost always referred to as Grand Theft Auto, even if the vehicle was a low value, perhaps due to being scrapped.