A link can be absolute or relative. An absolute link shows the full URL of the page being linked, whereas a relative link only shows the part after the domain.
Example of an absolute link:
<a href=”http://example.com/folder/filename.html“>Click here</a>
Example of a relative link:
<a href=”../folder/filename.html“>Click here</a>
Whilst both versions of the link will work, due to potential issues with canonicalisation, it’s generally best to use absolute links rather than relative links where possible.