URL shortening is a technique on the World Wide Web in which a Uniform Resource Locator (URL) may be made substantially shorter in length and still direct to the required page. This is achieved by using an HTTP Redirect on a domain name that is short, which links to the web page that has a long URL. For example, the URL "http://en.wikipedia.org/wiki/URL_shortening" can be shortened to "http://tinyurl.com/urlwiki". This is especially convenient for messaging technologies such as Twitter and Identi.ca which severely limit the number of characters that may be used in a message. Short URLs allow otherwise long web addresses to be referred to in a tweet.