Organic search rankings refer to the rankings of websites that appear on the SERPs as a result of search engine algorithms. Paid search rankings, on the other hand, are the rankings of websites that appear on the SERPs due to paid advertising. Paid search rankings are typically found at the top or bottom of the SERPs, and the ranking is determined by the amount the advertiser is willing to pay for each click. Here’s a thorough comparison between SEO and PPC that we posted some time ago.