Search engine optimization (SEO) is a process of optimizing your website with the goal of improving your rankings in the search results and getting more organic (non-paid) traffic. SEO aims to direct more traffic to your website from members of your target audience. These are consumers who are actively searching for the products and services you offer, as well as users searching for more top of the funnel content.
Search engine optimization focuses only on organic search results and does not include PPC optimization. Both SEO and PPC are part of Search Engine Marketing.