Metering is what it is called when you take a reading with your light meter
. Whether you actually see the light meter reading or not, unless you have camera with only one setting (like a disposable or pinhole camera), your camera has a light meter. When you point your camera at an object and press the button part way down, the light meter reads the amount of light reaching the film/sensor.
The vast majority of cameras meter purely off of the exact center of the frame. This means that if the center of the image is brighter than your main subject, your subject will be underexposed. SLR type cameras often allow the photographer to select the type of light reading the meter will use.
- Center-weighted Average
- Single Point Selection
This allows the photographer to select a reading method more consistent with his/her own shooting style. Even in cameras that do not allow the photographer to manually select the metering style, some cameras are beginning to use a smart metering algorithm that allows the camera to meter off of the obvious subjects in a frame rather than purely off of the center. This does help but it is important you know WHERE your camera is taking its light reading from.
Once you know where the light meter is taking a reading from you can adjust your shutter speed/aperture setting accordingly, or you can force the meter to take its reading where you want it to by pressing the shutter button halfway down when properly pointing at your selected metering spot. If you meter off of a bright blue sky, the hawk that is your actual subject will be underexposed/dark.