In "Shutter Priority" mode, you can select the shutterspeed over the available range and have the camera calculate the best aperture to expose the image correctly. Shutter speed priority is often used to create special effects such as blurred water on a river/waterfall or to freeze action in action scenes as illustrated in the shutterspeed topic of this glossary.
This article is written by Vincent Bockaert,
author of The 123 of digital imaging Interactive Learning Suite
Click here to visit 123di.com