URI

aka Uniform Resource Identifier

http://gbiv.com/protocols/uri/rev-2002/rfc2396bis.html

http://www.ietf.org/rfc/rfc2396.txt

in-process draft partially by Tim Bray: http://www.apache.org/~fielding/uri/rev-2002/rfc2396bis.html

http://www.w3.org/DesignIssues/Model.html

typically called URL - URL refers to the subset of URI that identify resources via a representation of their primary access mechanism (e.g., their network "location"), rather than identifying the resource by name or by some other attribute(s) of that resource

related is URN

http://www.w3.org/Addressing/

http://www.linktionary.com/re/urn.html

http://www.utoronto.ca/webdocs/Official/uri.html

http://uri.net/

Mark Nottingham on what non-alphanum chars should be encoded or not in paths and query strings.

John Gruber gives a Regular Expression for matching URI-s. Plus follow-up.

also Upper Respiratory Infection