Pay-per-click (PPC) advertising is search results returned to the searcher (or appearing on a website) that have been paid for by the owner of the website that the advertising links to. Usually, they are “paid for” by the advertiser only when they are clicked on.
In general terms, when a search engine has been made aware of the existence of a website, they will often send their “robot” to “crawl the site. The robot follows links on the site (usually from the home page) to lower level pages on the site. It catalogues keywords and other information on the site and stores this information in the search engine’s database. This information then determines the relevancy of the website in the event particular terms are used in the search engine’s search function.
Organic Search Results are search results that are returned to a searcher when using a search engine that have not been paid for by the owner of the listed website . Organic search results are developed by search engines through the process of crawling websites. On Google, for example, these are (predominantly) the search results down the left hand side of the search page.