You can create alternative text (alt text) for shapes, pictures, charts, tables, SmartArt graphics, or other objects in your Office document. Alternative text helps people with screen readers understand the content of pictures. When you use a screen reader to view your document, or save it to a file format such as HTML or DAISY (Digital Accessible Information System), alternative text appears when you move the pointer over a picture in most browsers.
Note: Unless you have a complex chart or table, you will usually want to enter text in just the Description box. When you have complex content to describe, then filling in the Title field is useful so reading the full description isn’t necessary unless desired.
Enter an explanation of the shape, picture, chart, table, SmartArt graphic, or other object in this box. This box should always be filled in.
Enter a brief summary in this box. This box should only be filled in if you are entering a detailed or long explanation in the Description box.
For example, suppose you have a table that shows the population of ducks by month for the year 2010. Your Title could be: "Table describing the duck population in 2010". And in the Description box, you could enter: "Month-by-month data describing the duck population in 2010. In March, the population of mallards rose 30%, breaking the consistent trend of 5% growth between January and June. Two consecutive months of 0% growth of penguins starting in August were also nonconforming."