The part of an HTML tag that describes an image. Alt tags are used to clearly define the contents of images for search engines.
An Alt Tag Description
The file name bklnbrdg.png is mildly descriptive but nothing a search engine will deal with. However, "Brooklyn Bridge" is very descriptive.
The Anchor Tag Counterpart
The anchor tag creates a hyperlink to a Web page, but the viewer sees "Sample Products" as a description of the link. See HREF