2. Page 2 SEO + PPC = $$$$$ A recent MarketingSherpa study shows top organic positions are clicked 20 percent of the time and top paid-advertising positions are clicked 10 percent of the time. However, if a site has a top organic position and a top paid-advertising position, the links to the site are clicked 60 percent of the time. It's an unusual situation: 10 + 20 = 60.
3. Page 3 What is SEO? Search Engine Optimization (SEO) is the process of improving the volume or quality of traffic to a web site from search engines via “organic" ("natural " or "algorithmic") search results. - Wikipedia
34. Search engines may have difficulty crawling, indexing, and extracting the content of your site if you have broken HTML or a poorly structured codebase.