A "stop" is a relative measurement of light.
The term "stop" is used in every aspect of photography to represent a relative change in the brightness of light.
For example: If you start with a single light bulb
Double the light is one
stop brighter (+1 stop)
Stops are interchangeable
The following chart shows common exposure settings. For the sake of example, the default "exposure" is set to 1/60, f8, ISO100. Don't worry about the numbers for now, because one step = one stop, regardless of which setting you move.
The Red line is the correct exposure, any combination of shutter speed and aperture will give the correct exposure.
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