When using spot metering, the camera only takes into account a certain spot of the image to calculate the exposure. It is usually the center of the image that it focuses on mostly center of the scene, but some cameras enable you to choose a different spot.
Spot metering is ideal when the image consists of objects that vary greatly in lightness. Spot metering allows you to ignore certain parts of the image and lets you focus on the main subject for the proper exposure. If it is used with a neutral gray card, a spot meter can simulate an incident light meter. With advanced microprocessor technology, spot meters are also available for use with electronic flash along with ambient light. Spot meters usually start at a few hundred dollars.