Search Engine Optimization (SEO) can be defined as a cluster of tactics and strategies used to ensure that a website is accessible to a search engine and improves the chances through which the website will be found by the search engine.
Therefore, the purpose of SEO is to obtain a high-ranking placement in the search results page of a search engine (e.g. Google, Yahoo, Bing). Internet users often don’t click through pages and pages of search results, so where a website ranks in a search is very important for directing more traffic toward the site.
Search Engine Marketing (SEM) represents a broader term than Search Engine Optimization (SEO), and is used to encompass different options available to use a search engine’s technology, including paid ads. SEM is usually used to describe acts associated with submitting, researching and positioning a website within search engines. Furthermore, it includes things such as search engine optimization, paid listings and other search-engine related services and functions that will certainly increase exposure and traffic to a website.
Thus, the difference between SEO and SEM is simply that Search Engine Optimization represents a part of Search Engine Marketing. A common element is that both processes aim in increasing visibility in search engines. As we said before, SEO is about optimizing the web property to get better rankings in the search results while SEM goes beyond SEO.
Another important fact is that SEO and SEM are not competing services. Due to the fact that SEO is considered a subset of SEM services, if you want to conduct business on the online environment you have to be visible in both organic and advertised links, which means you should use both SEO and SEM.