Alt text (Alternative text)
A short text description of an image, announced by screen readers and shown when the image fails to load.
Alt text lives in the HTML alt attribute and is the most common accessibility issue on the web. Meaningful images need descriptive alt; purely decorative ones need an empty alt="" so screen readers skip them.
It maps to WCAG 1.1.1.
Example
<img src="cat.jpg" alt="A tabby cat asleep on a keyboard">