You can use this to write a text description for people who can't see the item. The description should be enough for them to understand the purpose and information given by the media item. This is vital for blind users and other people using screen-reader software or text-only browsers.
You can use this to show a label that shows next to the item for all readers. This is often used to explain why the item is relevant to the context in which it is shown. It should be succinct and informative.
