SEM is a process of gaining traffic to the website by purchasing ads on the search engines. It is one of the most efficient ways to build your business in a growing competitive market. There are mainly two forms of search engine marketing services, first is search engine optimization (SEO) uses the technique to boost search engine ranking in unpaid search results. Second is (Pay per Click) PPC it is nothing but getting the traffic to the website by paying some amount to the search engine.
source