Glossary Term: Search Engine Ranking Position (SERP)
Search engine ranking position (SERP) refers to the display position of a site when user perform searches through search engines using certain keywords. In theory, most users will only click through the top 10 search results. So in order for user to find your web-site through search results, you will need to either perform Search Engine Optimization (SEO) on your web-site, or pay to place an advertising ad beside the search results.
Click through from organic search results are free traffic. If your site is able to achieve a high search engine ranking position on a popular keyword, you could will save a lot of your advertising cost.