It's an HTML tag that provides alternative text when non-textual elements (typically images) cannot be displayed.

What are the benefits of updating my alt text image tags? 

There are three main benefits to using alt text image tags: 

• If an image is broken, the alt text image tag will be displayed instead of a broken image symbol.
• If a visually impaired person is using a special browser that reads text on websites, it will read the alt image tags.
• By including keywords in of your alt text image tags, search engines get a better idea of what your website is about.Your website's images are also more likely to show up if someone does an image search for your selected keywords.