Alt text stands for alternative text. It is also known as alt attributes or alt descriptions. You will also find it as alt tags, though this is technically incorrect.
Alt text is used a part of an HTML code used to describe the appearance of an image on a page. They provide a context and image descriptions so search engines can index it properly.
Alt text is used to make the web more accessible. People who are visually impaired and use screen readers can have the software read the alt text to gain a better understanding of the page.
Alt attributes will be displayed when an image file cannot be loaded.
Using alternative text in your images makes it possible for all users to understand what the content of your site is whether they have limited use internet, or have a visual disability. Alt text improves user experience, and that is always good for SEO. But beyond that, it provides crawlers with the necessary information to classify your site’s visual content. This allows search engines to index it properly and rank your website for the correct keywords.
What makes alt text good? This is what Google has to say about it:
“When choosing alt text, focus on creating useful, information-rich content that uses keywords appropriately and is in context of the content of the page. Avoid filling alt attributes with keywords (keyword stuffing) as it results in a negative user experience and may cause your site to be seen as spam.”
If when you read it, you can picture the image in your mind, then you have created a good alt text. If you can seamlessly incorporate one of your keywords in it, even better. However, remember that spamming is heavily frowned upon by search engines. So, if you already have a good keyword density in your text, there is no need to overdo it.