In photography, exposure is the amount of light per unit area reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance.
There is some different types of exposure, for example:
UNDER EXPOSED PHOTOGRAPHY
Under exposed photography is the picture which has the small amount
of light and it can be very dark or a bit dark.
Also we can change the darkness to make it darker or whatever how
dark we want in to be.
OVER EXPOSED PHOTOGRAPHY
Over exposed photography is the complete opposite of the underexposed.
An image that is brighter than it should be can be considered overexposed.
When too much light is allowed during exposure, the result is an overly bright photograph.
PERFECT EXPOSURE
Perfect exposure is the original exposure which is the middle between underexposed ad overexposed, and it's the normal exposure not dark and not bright.