A written description of an image, read aloud by screen readers, shown when the image fails to load, and used by search engines to understand what the picture shows.
Alt text is first an accessibility requirement — for a visitor using a screen reader it is the only way the image exists at all. In Canada, accessibility obligations for business websites are tightening, and this is among the cheapest items to get right.
It is also how images get found in image search, which matters more than people expect for trades and retail, where customers search visually for finished work.
This comes up most often in Technical SEO & Site Speed. Crawling, indexing, speed, structured data and site architecture — the plumbing that decides whether your pages can compete.
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