I learnt this from https://itnext.io/html-underrated-tags-119ef3e45b94. This is an amazing post.
So basically, the tag is the
<base></base> tag. It is used like this:
<base href=”https://www.example.com/" target=”_blank”> <a href="a-post.html">A post</a>
So if the base is mentioned earlier, all the relative links will be according to this. This is very useful when you are using a tool like site sucker, which saves files from a webpage. Some resources like images might not be correctly displayed if you saved a single file locally, but it will if you add the base tag, telling the html file that all the media files with relative links are from this webpage.