the text that appears when a mouse hovers over an image. Alt tags should convey what the graphic is for or about, and should contain relevant keywords. ALT tags are added to images in order to describe the content of the images, and aid with categorization.

The alt tag of the image below is "Organic Search Solution".  If you hover over the image you will be able to see the alt text.  As a reminder, by default, alt text is not visible when using the FireFox web browser.