This is ISO.
It's the setting on your camera which controls how your sensor records light.
The higher the ISO number, the more sensitive-to-light it is.
In low light situations, one would normally TURN-UP the ISO to a higher number - because the light is low and your camera has to PULL IN the light.
Conversely, on a bright day outside, one would be able to TURN-DOWN the ISO because the light is entering the camera quickly...because it's bright.
For now, simple as that.