Image alt text is the text value of an HTML image element’s alt attribute, originally intended to describe an image to users who cannot see it — including screen readers and text-only browsers. For SEO, alt text is the primary way search engines understand what an image depicts, making it important for image search visibility and for giving additional topical context to a page. Best practice is to write alt text that describes the image accurately in natural language, incorporating a relevant keyword where it fits naturally, without keyword stuffing. Decorative images — such as borders or spacer graphics — should have empty alt attributes (alt="") so screen readers skip them. The alt attribute is distinct from the image file name and surrounding caption, both of which also contribute signals but carry less direct weight.