The Facebook "Like" button is a feature that allows users to show their support for specific comments, pictures, wall posts, statuses, or fan pages. Added in February 2009, the "like" button allows users to show their appreciation for content without having to make a written comment. While pages originally gave users the option to "become a fan" of them, Facebook replaced this option with a "like" button in April 2010.
After a user "likes" something, their news feed is updated, letting their friends know what pages they "like." Facebook has also made it possible for web sites to add "like" buttons directly to their sites. If a user clicks a "like" button on a web page, their news feed will be updated with a link to the web page.
According to Facebook, the “Like” button allows you to target ads to people who like your content.
Peter Garety suggests there are “Three Advantages of the Facebook Like Button You Should Know About.”