Facebook Social Plugin is basically a widget you can add to your website to extend the benefits of your Facebook marketing efforts beyond Facebook. It's a way to get more marketing mojo out of Facebook on your own website, and with a social network that has amassed over 800 million active users.
There are a number of Facebook Plugins that you can utilise to market on your website:
Comments Box: The Comments Box is a plugin that allows visitors to comment on your website. It leverages social signals to highlight the highest quality comments from users and are ordered to display the most relevant comments from friends, friends of friends, and the most Liked or active discussion threads.
Activity Feed: Facebook's Activity Feed plugin displays the most interesting recent activity taking place on your website. The feed features content users have Liked on your site, content from your site that users have shared on Facebook, and content that users have commented on in a page's Comments Box (if installed).
Recommendations Plugin: The Recommendations Plugin displays personalised recommendations to users based on all the social interactions with URLs from your website and the users' friends' activity.
Like Box: The Like Box enables businesses to attract new Likes (AKA fans) for their Facebook business page directly from their website. Site visitors can like their page with just one click without needing to leave the site to visit Facebook. The Like Box also shows how many other total Facebook users like the page, how many of the individual visitor's Facebook friends also like the page, and highlights posts recently published to the Facebook page.
Face Pile Plugin: The Facepile Plugin displays thumbnail-sized profile images of Facebook users who have Liked a particular page on your website or signed up for your site via the Registration Plugin. he Facebook Plugin is a great tool for taking advantage of the effects of social validation/proof. If a visitor recognizes a face of a friend who has Liked a particular piece of content on your website, it will add an element of trust and credibility to that content and your brand, and may even encourage them to Like the content, too.