An Absolute Link is a hyperlink that has a fully-qualified URL, therefore, containing the protocol of website, whether that be http or https. Below are some examples of absolute links:
As you can see, the URL’s contains the full address of the website pages, this includes all of the information needed to find a particular site on the web, therefore, your browser will navigate directly to the http version of the site. This can also be used for the always-ssl version, https. above the fold
Absolute links must be used to link to other websites, otherwise, the web browser won’t know where to take you. However, they can be used internally to link to other pages within your site, but it isn’t best practice as it will take the browser longer to navigate to the fully-qualified URL, plus it makes things messy behind-the-code.
Therefore, webmasters may decide to use a relative link, below are some examples:
You can learn more about the use of a relative link here.