goo.gl is a web address shortener.
If you go to the web address goo.gl, you can copy-and-paste a long web address into the bar at the top and hit the "Shorten URL" button - it will spit out a much shorter URL. This makes it a lot easier for people to copy down the address if they need to type or write it down.
Because goo.gl is linked to your Chrome account, it will keep a running list of all the pages you shorten, so you can always go back to look up shortened addresses. While on the goo.gl page, if you click on the check-box at the beginning of a previous long URL, you'll see an image of what that page looks like (in case you forgot which page it was).