RFC 3986:

Berners-Lee, et al.         Standards Track                     [Page 4]
RFC 3986                   URI Generic Syntax               January 2005

 Resource

    This specification does not limit the scope of what might be a
    resource; rather, the term "resource" is used in a general sense
    for whatever might be identified by a URI.  Familiar examples
    include an electronic document, an image, a source of information
    with a consistent purpose (e.g., "today's weather report for Los
    Angeles"), a service (e.g., an HTTP-to-SMS gateway), and a
    collection of other resources.  A resource is not necessarily
    accessible via the Internet; e.g., human beings, corporations, and
    bound books in a library can also be resources.  Likewise,
    abstract concepts can be resources, such as the operators and
    operands of a mathematical equation, the types of a relationship
    (e.g., "parent" or "employee"), or numeric values (e.g., zero,
    one, and infinity).