Organic Search Listings are results based on factors such as keyword relevancy within a web page.
These are the listings generally found on the left hand side in search engines such as Google, Yahoo! and MSN, and are not influenced by direct financial payments, only by effective Search Engine Optimisation.
The algorithm for Organic Search Engine Listings often changes, to stay ahead of disreputable organisations attempting to cheat their way to the top, although a solid approach to Search Engine Optimisation will always avoid being banned.