An organic listing takes the approach of optimizing your search results internally or through a company that provides Search Engine Optimization, where you do not have to directly pay a search engine. The natural search results produced from an organic listing are derived from search algorithms and are a direct result of SEO.
A paid listing is where you provide the funds to deliver your listing to a search engine. Paid listings are usually limited to banner advertising and PPC (Pay Per Click). These concise listings usually contain 2-5 word titles sub headed by two lines of text.
The major difference between these two types of listings are that organic listings, being that they are extracted from search engines, give the creator little control over what marketing message is being formulated. On the other hand, paid listings are the direct representation of exactly what the advertiser wanted to convey.
SEO and SEM experts are constantly debating the theory that a combination of these two listing types can create an immediate impact and lead to lasting results. The only concrete fact is that you will never know what works until you utilize these options.