SMO is a short hand for Social Media Optimization.
It is the methodization of social media activity with the intent of attracting unique visitors to website content. SMO is one of many online methods of website optimization.
There are two categories of SMO/Social SEO methods:
(1) Social media features added to the content itself, including: RSS feeds, social news and sharing buttons, user rating and polling tools, and incorporating third-party community functionalities like images and videos
(2) Promotional activities in social media aside from the content being promoted, including: blogging, commenting on other blogs, participating in discussion groups, and posting status updates on social networking profiles.