What is the definition of an absolute URL (fully qualified?)

Question

There are (at least) three ways to link to a resource:

1. href="foo/bar.html"
2. href="/foo/bar.html"
3. href="http://example.com/foo/bar.html"

The first is a "relative url", no problem. But I've seen (2) and (3) both referred to as an "absolute url". Which is correctly termed an "absolute url", and what is the proper name of the other?

(Bonus points for references to relevant standards or other official documentation.)

Answer 1

RFC 3986 defines Uniform Resource Identifiers.

A relative reference that begins with a single slash character is
termed an absolute-path reference. A relative reference that does
not begin with a slash character is termed a relative-path reference.

1. href="foo/bar.html" is a relative reference, specifically a relative-path reference.
2. href="/foo/bar.html" is a relative reference with an absolute path
3. href="http://example.com/foo/bar.html" is an absolute URI
4. href="//example.com/foo/bar.html" is a network-path reference

A relative reference that begins with two slash characters is termed a network-path reference; such references are rarely used.

Answer 2

"Absolute URLs contain a great deal of information which may already be known from the context of the base document's retrieval, including the scheme, network location, and parts of the URL path."

https://www.rfc-editor.org/rfc/rfc1808

The number (2) is an absolute path, the (3) is an absolute URL.

Answer 3

I like the W3's description found here:

A URL is an absolute URL if resolving it results in the same output regardless of what it is resolved relative to, and that output is not a failure.

It doesn't bring up scheme, path, or any other concepts like that, but basically just says that the same input always brings the same output. You can only say that about #3.

I wouldn't get too caught up in the technicalities though - #2 is still absolute if your universe is the website. Also something like //example.com/foo/bar.html is absolute if your universe is the scheme. I think the word "absolute" in those cases is still meaningful from a developer's perspective.