In a few words smo is using social media to bring traffic : http://en.wikipedia.org/wiki/Social_media_optimization
SMO is a set of method for generating publicity through social media, online community and community website...
SMO is about the strategies used to set up Social Media components on your website that allow your customers to interact and participate with you during their online experience. The whole point is to make your site more accessible to your visitors by allowing them to interact with your content via the following means.
SMO shall not be mixed with SEO. Businesses that have a solid foundation and want to keep their customers engaged must use SMO.
Social media optimization is in many ways a technique of Internet marketing where word of mouth is created not through friends or family but through the use of networking in social bookmarking, video, photo sharing and other media related websites. In order to get your name out with social networking, you must become one of the community rather than an advertiser to the community. Create a profile on any social media site and link up with people of similar interests. If you have a well branded product or a faithful customer base, encourage your group members to spread the word.
Anyone can start a YouTube or Twitter account, but to fully utilize their potential you need to master SMO.
Site Management Organization; performs and manages research for individual Investigative Sites. SMOs' responsibilities include patient recruitment ...
SMO stands for Social Media Optimization. It is a part of off-page optimization. In it, we join different social media channels (like twitter, facebook, etc.), collect followers/friends and share our the links of our sites, any latest news,ideas, press release or event announcing with them. It cause traffic increasing to your site. More information you can read from here: Social Media Optimization-1 Social Media Optimization-2
Just remember that social media isn't just for backlinks, but to engage in a conversation. Whether Facebook, Twitter, Digg, or even Youtube, there should be a constant stream of communication between yourself and your viewers/readers/fans.