Regular videos are played at a rate of 24 frames per second. This is fast enough to fool us into thinking that the motions are fluid even if the images were taken at discrete intervals. Some cameras are capable at shooting at a much higher rate such that the resulting images can be played for a longer period compared to the actual scene. For instance, a footage may be slowed down up to 4x or more so that quick changes are easier to see.
These high speed cameras are capable of recording 1,000 frames per second and up. They are used in various settings including car factories that want to study the results of crash tests. Multiple cameras cover different angles. The crash often happens extremely fast so slowing things down allows the engineers to see the behavior of the test dummy and the vehicle structure during the crucial moments.