A hot rod is a specific type of automobile that has been modified to produce more power for racing straight ahead. The hot rod originated in the early twentieth century in the United States and continued in popularity over several decades until a decline in the 1970s. It was then that street rods took over; the difference between a hot rod and a street rod is the intended purpose of the vehicle.
Hot rods were built for racing, while street rods are built mostly for show and driving around town. Common modifications of early hot rods included engine replacements, body streamlining, and other body modifications.