Macro or Close-Up Preset Camera Mode

Macro (also called Close-Up) mode is almost always represented by an image of a flower of some sort. This mode tells your camera that you want to be very close to your subject in order to fill the frame with the subject. This setting works with your camera lens to allow it to focus from a very short distance. In some cases, only a few inches from the subject. While this setting allows you to get some great shots of small objects, be aware that the depth of field becomes very small in macro photography.

This preset is best used for its original purpose of getting very close to small objects and does not have a lot of alternative uses.

Source : http://photography.about.com