A custom car is a passenger vehicle that has been substantially modified in either of the following two ways
1. A custom car may be altered to improve its performance, often by altering or replacing the engine and transmission
2. A custom car may be a personal "styling" statement, making the car look unlike any car as delivered from the factory.
Although the two are related, custom cars are distinct from hot rods. The extent of this difference has been the subject of debate among customizers and rodders for decades. Additionally, a street rod can be considered a custom.
Hot rods are typically old, classic American cars with large engines modified for linear speed. The origin of the term "hot rod" is unclear. For example, some claim that the term "hot" refers to the vehicle being stolen. Other origins include replacing the engine's camshaft or "rod" with a higher performance version.
The term has broadened to apply to other items that are modified for a particular purpose, such as "hot-rodded amplifier".