Google +1 : Java Glossary

Not to be confused with Google Plus, is a Google service that lets you recommend a page as unusually useful. Clicking the +1 icon asks Google to bump the page up in the Google search ranking. The number beside the icon in the bubble tells you how many other people have recommended the page. You can see the icon at the top of each page next to the Babelfish icon. It does not appear when you are viewing the page offline. You must be logged in to Google to vote. When you get the code for the button, make sure you set the advanced options to ensure HTML5 (Hypertext Markup Language v 5) compliance.

To install it on your own websites, you must add some JavaScript where you want the button to appear, some more to at the end of the page. The button does not appear when you are offline.