Search engine optimization (SEO) is the process of improving the volume and quality of traffic to a web site from search engines via "natural" ("organic" or "algorithmic") search results for targeted keywords. Results are on the left section of the SERP.
Pay per click (PPC) is an advertising model used on search engines, where advertisers only pay when a user actually clicks on an ad to visit the advertiser's website. Results are on the right section of the search engine results page.
