When a search engine returns its search results, it gives you two types: organic and paid. Organic search results are the Web page listings that most closely match the user’s search query based on relevance. Also called “natural” search results, ranking high in the organic results is what SEO is all about.
Paid results are basically advertisements — the Web site owners have paid to have their Web pages display for certain keywords, so these listings show up when someone runs a search query containing those keywords.
On a search results page, you can tell paid results from organic ones because search engines set apart the paid listings, putting them above or to the right of the organic results, or giving them a shaded background, border lines, or other visual clues. The following figure shows the difference between paid listings and organic results.
The typical Web user might not realize they’re looking at apples and oranges when they get their search results. Knowing the difference enables a searcher to make a better informed decision about the relevancy of a result. Additionally, because the paid results are advertising, they may actually be more useful to a shopping searcher than a researcher (as search engines favor research results).