a camera that is attached to a car's dashboard (= the part that contains some of the controls used for driving and the devices for measuring speed and distance) in order to record what is happening on the road that the car is driving along

Dash cams can record your journey and provide invaluable evidence in any driving incidents. 行车记录仪可以记录行车过程，并在发生事故时提供宝贵的证据。