A URL shortener is an online application that allows the user to enter a full URL for any specific web page, click on a button, and automatically shorten that URL to an abbreviated version that is approximately 10-20 characters. The purpose of URL shorteners is three-fold:
First, it's very useful for microbloggers, such as Twitter users, who like to share URLs in their posts. However, with a 140-character limit on sites like Twitter, it's often difficult to include a lengthy URL along with an explanation of why you're sharing it.
Second, URL shorteners are helpful because they can preserve a link to a specific web page even if the URL to that page changes in the future. However, it's not guaranteed that the shortened URL will work if the original URL changes.
Third, some URL shorteners allow you to track the number of clicks your shortened link gets allowing you to analyze the type of traffic you're generating to your website, blog, etc. from your links on Twitter, Facebook, and so on. This allows you to understand in greater detail where your promotional efforts are having the biggest impact.
