ALT Tags
HTML tags that are used to describe website graphics by displaying a block of text when a mouse hovers over it. Search engines are generally unable to view graphics or distinguish text that might be contained within them, and the implementation of an ALT tag enables search engines to categorize that graphic and the page itself, which also allows for more keyword usage within reason. There is also talk that business websites will all eventually be required to utilize ALT tags for all pictures to comply with certain American Disability Act requirements.