Search Engine Marketing
Search Engine Marketing (SEM) is basically the science and art of getting targeted traffic (free and paid) to your website from Google, Yahoo, Bing or other search engine networks. It can also defined as a form of internet marketing that involves the promotion of websites by increasing their visibility in the search engine networks.
Search Engine Optimization
Whenever you type a query in any search engine and hit the "search" button you get a list of web results which contain that query term. Users normally tend to visit the websites that are at the top of this list as they perceive those to be more relevant to the query. If you have ever wondered why some of these websites rank better than the others then you must know that it is because of a powerful internet marketing technique called SEO.
Social Media Marketing
In analogy to search engine marketing explanation we can similarly state that Social Media Marketing (SMM) is basically the science and art of getting targeted traffic (free and paid) to your website from Facebook, Twitter, LinkedIn, YouTube, Google+ or other social media networks. It can also defined as a form of internet marketing that involves the promotion of websites by increasing their visibility in the social media networks.