SEO is a Search engine optimization,its a set of best practices that help search engine crawlers to visit the website. It allows search engines to show your website to people who are looking for your products or services. It focuses on organic search results and depend upon the Google algorithm for ranking websites.

SEM is search engine marketing,the full set of tactics that can grow your visibility on search engine results pages. It can include paid techniques for the promotion of website. When you buy search ads, your business is guaranteed a presence within search results.