The term 'four-door auto' is a type of vehicle that has four doors and is powered by an internal combustion engine. The most common type of four-door auto is the SEDAN, which is a car with four doors and a fixed roof. Sedans are typically larger than other types of cars, such as hatchbacks or coupes, and are often used for family transportation. They are also popular for business use due to their spacious interior and comfortable ride.