What is light metering?
Essentially it’s the internal workings of the camera that measures how much light is coming in and determines how bright a scene should be in your photo. The three general types of light metering modes are, evaluative, center weighted average and spot metering. Each of these modes look at different parts or combinations of parts of the image to determine how to adjust the cameras brightness.
To explain this further with some great examples, check out this article;