Search engine saturation is a term you don’t hear too many optimization folks talking about any more. But it’s a useful term and you need to know what it is. In a nutshell, it refers to the number of pages you have indexed in the search engines. Search engine saturation is your gauge for how effective you are in getting search engine listings. It’s one of the gauges for how effective you are at search engine marketing in general. source: http://www.searchengineoptimizationjournal.com/2009/04/24/search-engine-saturation/