The term 'road rig' is a colloquialism for a SEMI-truck, which is a large vehicle used to transport goods and materials over long distances. The term 'SEMI' is a four-letter word that is often used to refer to this type of truck. A road rig typically consists of a tractor unit, which is the cab of the truck, and a trailer, which is the cargo-carrying portion of the truck. Road rigs are an important part of the transportation industry, as they are used to move goods from one place to another.