Facebook Like & Send
Formerly known as the " Become a Fan" Facebook button, the Like button lets a user share your content with friends on Facebook. When the user clicks the Like button on your site or a particular post or article, a story appears in the user’s friends’ News Feed with a link back to the article, post or the page on your site it was clicked on.
Facebook’s content sharing options are the most popular and widely used Social Media tools on the World Wide Web; they give your content a sheer unlimited potential for exposure via Facebook’s ever growing member network.
Just recently, in April 2011, Facebook announced it will replace it’s similarly popular "Share" Button with a new version, the "Send" Button which allows user to share content with only select friends instead of sharing it on their profile.
Facebook’s official announcement The Send Button, Because Sometimes It’s Private explains why they are moving away from "unfiltered" sharing.