“Exposure” is the choices made in the Exposure Triangle and how it looks in the final picture. An image is properly exposed when it is not too bright and not too dark.
Here is an image I took on July 9, 2014.
The exposure triangle settings for this image were:
Shutter Speed: 1/800 sec
Equally good exposures could have been had with a shutter that is half as fast and an aperture that lets in twice as much light, that is, make the aperture smaller by one stop and make the shutter speed slower by one stop:
Shutter Speed: 1/400 sec
Here is a table that shows lots of exposure triangle values that would have worked well:
|Triangle||Ex 1||Ex 2||Ex 3||Ex 4||Ex 5||Ex 6|
I chose this image because there would not be much difference in the final photograph for any of these choices.
Why does one choose one set of values over another one? That is the $10,000 question! For now, let’s say that the answer to that question is, “It depends.”
The full answer to that question is addressed in the next section.
 Of course, sometimes you WANT an image to look dark or to look light. We’ll skip that for now.