In my notes I had this called "site relative" following this Stack Exchange post: https://webmasters.stackexchange.com/a/71376/12374

But you're right; relative by itself would refer to relative to the current location. Error on my part in not being specific enough. In retrospect "site relative" is not good terminology.

It's URL relative.

Example, for "http://mysite.com/dir/page1.html":

    * Relative:     "../other_dir/page2.html"
    * URL relative: "/other_dir/page2.html"
    * Absolute:     "http://mysite.com/other_dir/page2.html"