Search Engine Optimization (SEO) has traditionally been thought of as a component of the umbrella term, Search Engine Marketing (SEM), encompassing both paid AND organic tactics. Today, SEM is used to refer exclusively to paid search. According to Search Engine Land, Search Engine Marketing is “the process of gaining website traffic by purchasing ads on search engines,” while Search Engine Optimization is defined as “the process of getting traffic from the free, organic, editorial or natural search results on search engines.”
So, rather than viewing SEM as an umbrella term encompassing SEO, it’s more accurate to view SEM (paid search) and SEO (organic search) as separate entities to use as part of your Search Marketing arsenal.