It refers to an attribute of HTML that provides an alternative to elements like images.

It is common to see that ALT texts getting omitted from individual pages on the web. This could vary from personal pages that are smaller in size to the ones that belong to larger sites of corporate companies. If they are used properly, ALT texts can be pretty useful. There are many things ALT text can do: Disabled people can have an easy access through these texts, they will provide additional details for a given destination or for an image that is hyperlinked. In case of slower connections, these texts will assist in easy navigation over sites that are enriched with different graphics.