SEO means optimizing your website and web content for search engines like google, bing, yahoo, baidu, yandex, etc. SMO means optimizing your website and web content for social media platforms like facebook, twitter, linkedin, instagram, etc. SEO will get you organic traffic, SMO will get you referral traffic. The primary purpose of SEO is to improve search engine ranking, where as the motive of SMO is to make the content viral on social site.