Bit.ly, is.gd, ow.ly.
Many of us have used URL shorteners at some point or another to share a link with someone. They can take an ungainly URL (such as one found on an e-commerce site that contains dozens of characters,) and turn it into a quick and simple link that is small and compact enough to fit into SMS, Twitter, or email messages.
But what happens when the URL service has a technical problem? You may have no way to recover your URL.
For most cases, I use URL shorteners for one-off URLs or things I’ll only need one time. I try not to use them for things that I may need for long term, like links to a product that I recommend often or links to old articles I’ve written. If you use a shortened URL enough, it can become the URL for your content, which is fine as long as it’s working. But when it goes down (and services do go down,) you have no control over the URL any more.
Keep in mind that URL shorteners are for convenience and portability, and not long-term content storage, and you should be alright.