Alt Text
Alt text is a written description of an image stored in the HTML, which screen readers read out and which is displayed when the image itself cannot be loaded.
In practice
Good alt text briefly describes the relevant content or purpose of the image in the context of the page, rather than repeating “image” or the file name; purely decorative images get an empty alt attribute instead, so that screen readers skip them. Meaningful alt text satisfies WCAG success criterion 1.1.1 and is part of Google's recommended best practices for images – it helps search engines classify what an image shows and is a visible mark of carefully maintained content.