An automatic dirt bike is like any other automatic motorcycle in the fact that power is transferred from the engine to the drivetrain via an automatic gearbox.
In short, it’s a motorcycle that doesn’t require changing gears with the use of a conventional manual clutch. The term “twist and go” is often used with automatic motorcycles because a rider can simply twist the throttle.
An automatic dirt bike specifically refers to an automatic motorcycle that’s designed for off-road riding, with long-travel suspension, off-road tires, and other accessories for improved riding across unpaved terrain.