Absolute URLs are internet addresses written as their full path to find a web page, image or anything else that has a path. This is opposed to a relative URL.

Relative URLs can only be used for internal linking, when creating a link to something on the same domain. Absolute links are always used when linking between different websites.

Example:

The absolute URL to this glossary entry is:
https://northrook.com/glossary/#absolute-url

As long as we're on the same domain, we can use this relative URL:
/glossary/#absolute-url