In the context of an OS (*nix, Windows), an absolute (or full) path is one that points to the same location on the file system regardless of the present working directory, e.g.
In the context of the web, an absolute path is synonymous with the URL. At the least, it includes the protocol, domain, and a path to a file or resource, for example:
http://www.sandra.me/homework/history.html. In this example,
http is the protocol,
www.sandra.me is the host, and
/homework/history.html is the path.