The Internet is full of websites - some with short URLs and some with very long URLs. A URL shortener shortens a long URL so that the website can be more easily accessed. Here is a list of useful URL shorteners.
Goo.gl is Google's official URL shortener. This URL shortener is useful because it allows you to track, in real-time, the clicks and referrers on any shortened URL.
TinyURL is one of the more efficient URL shorteners because, while you can't track the number of clicks and referrers on a TinyURL, it is widely accepted on multiple communities because you can assign custom short URLs.
Owly is the official URL shortener that Wikia uses.