Metering is used to calculate the exposure from the existing lighting conditions. Most DSLR cameras with have 3 metering modes:
Matrix metering (i.e. multi-zone, evaluative, honeycomb or segment metering) is the default camera metering setting. The camera measures the light intensity in several points in the scene, and then combines the results to find the settings for the best exposure. It’s ideal for most situations.
Spot metering measures a very small area of the scene (between 1-5% of the viewfinder area). This is usually the center of the scene, but some cameras allow the user to select a different off-centre point.
Center-weighted metering the meter concentrates between 60 to 80 percent of the sensitivity towards the central part of the viewfinder. The balance is then “feathered” out towards the edges.