To view and edit image metadata, go to the File ▸ File Info…menu item to bring up the image metadata edit window. From there you can navigate to the general, camera, IPTC, and everything categories to add, view, or remove information associated with your image.
According to the wikipedia entry on metadata, “Metadata may be written into a digital photo file that will identify who owns it, copyright and contact information, what camera created the file, along with exposure information and descriptive information such as keywords about the photo, making the file searchable on the computer and/or the Internet. Some metadata is written by the camera and some is input by the photographer and/or software after downloading to a computer.”
keywords: exif, data