SEO / SEM / SMM
Search Engine Optimization (SEO), Search Engine Marketing (SEM) and Social Media Marketing (SMM) are interrelated and as such cannot be defined in isolation. That is, while doing SEO a link posted on social media along with the content can be a valuable traffic earner and hence can get good ranking for the web page whereas a paid banner on a social media site can be a good SEM tool.
But, broadly speaking a non-paid form activities carried out for getting good ranking upon organic search on search engines is defined as "Search Engine Optimization (SEO)" where as a paid form of advertising is known as "Search Engine Marketing (SEM) or Pay Per Click (PPC) Advertising". Social Media Marketing (SMM) is marketing carried out on social media sites with or without making any payments to the social media sites.