Natural Search or Organic Search is where a website is listed by a Search Engine, such as Google, when a user types in a search word or phrase for example "IT Support London". It is the very opposite of ppc or pay per click which is a paid for listing, ie companies have paid Google to appear and are not listed through merit.

NAtural Search are search results that are found on the left hand side of the page when searching in Google.

The single greatest advantage of Natural Search over ppc is that more users click on links to websites listed in Natural Search before using companies that are paying Google.