Portrait Mode Automatic Setting
Many DSLRs and some compact digital cameras come with a portrait mode. While the specifics vary among manufacturers, the general idea is the same. Portrait mode will attempt to use settings that produce a blurry background and soft image. The idea is that most “standard" portraits are taken with these goals in mind.
The blurry background ensures that the subject is the focus of the picture and that the background does not provide a distraction to the viewer. Notice how in this picture, nothing behind the bride is recognizable. As a result, the brain will ignore the background and the full focus will be on the subject.
The soft image is a subject of some debate, but the theory is that softer photos are more flattering. Keep in mind that depending upon the abilities of your digital camera, these goals may not be achievable given the light and composition. So, this can be regarded as a best attempt only. The better the lighting and composition, the more likely the camera will be able to achieve these goals, so it can be a good way to test your setup.
Many cameras will also alter the default focusing method in portrait mode and some may also alter the method the camera uses to calculate exposure. Refer to your camera manual to find out if any of these changes apply to your portrait setting. If so, make a note of them and be sure you test the non-portrait values of these settings when you start using the manual modes.