Social media activities may include-->
- social networking
- blogging
- video marketing(on YouTube and other free sites)
- article promotions
Note:--->Social media optimization(SMO) ia all about creating the public profiling of the company so that brand awareness of the company could be increased as well as the net traffic to the companies website.It does not include the paid marketing compaigns on social media networks like making use of facebook ads!while these paid viral marketing compaigns are included in social media marketing(SMM).So SMM includes the paid social search while SMO does not include it.
Note:--->SMM(social media marketing) includes SMO(social media optimization) and placing ads on social media.
Note--->SEM(search engine marketing) includes SEO(search engine optimization) and PPC(pay per click) and PPM(pay per million impressions) etc in search engine page results.So SEO deals with the organic or free traffic to the website through search engines while SEM deals with both organic as well as paid traffic to the website through search engines.
Note--->SEO is the subset of SEM and SMO is the subset of SMM.
Note--->Now a days we usually use these terms interchangeably,though in exact meaning they are different!
There are many free SEO tools available like
http://tools.seobook.com/general/keyword-density/