Constant velocity (CV) joints are mechanical power transmission components which provide rotational power at various angles. They provide the same output velocity in relation to the input velocity independent of the angle they are operated at. This contrasts with most other joints, which may provide a different output velocity at sharper angles even with the same input velocity.
CV joints are commonly used in automotive drive systems in order to stabilize the vehicle on increasingly sharp turns. Automotive CV joints typically employ a Rzeppa joint design as shown below.
A Rzeppa joint. Image credit: Earl Morse
Industrial CV joints are typically used on CV shafts in pumps, dynamometers, rollers, generators, and within the milling and food processing industries.