The primary difference between the two is that Search Engine OptimizationOptimization (SEO) concentrates on optimizing a website to draw traffic from natural search results. 

On the other hand, Search Engine Marketing’s (SEM) objective is to increase exposure and traffic from sponsored and organic searches. 

In other words, paid and organic search results are the two main divisions of Google’s search results. Ranking your website in organic search results is the aim of SEO. In SEO, your focus should be on appearing high in natural search results. 

SEM is when you use both SEO and PPC to increase search engine traffic. SEM is a general word that covers PPC and SEO. Hence, SEO and PPC fall under the category of SEM.