Exposure
How much light a picture gathers: too much washes it white, too little sinks it in black.
See it in FX engine. Under Adjustments, move Brightness down and up and watch the ends clip.
In plain words
A camera gathers light for a short moment. More light makes the picture brighter, and less makes it darker. That amount is the exposure. Too much, and bright parts turn pure white with no detail left. Too little, and the dark parts sink into flat black.