Search engine saturation is a term relating to the number of URLs included from a specific web site in any given search engine. It is basically a metric to measure how effective you are in search engine listings. The higher the saturation level or number of pages indexed into a search engine, the higher the potential traffic levels and rankings.

Saturation implies there is a bar or metric that allows you to determine how much of something has been touched, absorbed, transformed, etc. With respect to search engine indexing, there are different types of saturation.

For example, given a list of X search engines, you achieve 100% search engine saturation if your site is found in all X search engines (although that is perhaps the crudest of metrics as it would be 100% even if one search engine indexes a single page whereas another indexed 1000 pages). Using that same list of X search engines, you can also (or alternatively) say you achieve 100% search engine saturation if and only if all X search engines index every page on your site.

Let’s say you have a website with 100 pages. If 90 of those pages are indexed at Google, 75 are indexed at Yahoo!, 80 are indexed at MSN, and 65 at Ask.com, and you’d say that your search engine saturation is a sum of those. That is, 310. You could include smaller search engines like Mahalo, Dogpile, and the several thousand others out there, but then counting pages would never end, so I just stick with the big 4. It doesn’t matter that you have cross over on the indexing. If 65 of the pages indexed at Yahoo! are also indexed at Google, that doesn’t change your raw number. Your SES is a cumulative rating.

Crawl saturation, which measures how much of your site a search engine actually fetches.
Index saturation is about how much of your site is listed in the search engine's index. There is no correlation between crawl saturation and index saturation because a search engine has the option of listing documents it has found links to but which it has not yet fetched.

For example, you could use a working definition for full index saturation that stipulates a page has been crawled and fully indexed by the search engine or you could stipulate that a page must simply have been fetched or you could stipulate that a page must have a cache link in the search engine-listings.

Most if not all site searches in Google produce limited results. That is, they won't show you all the pages that Google has crawled/fetched and they won't show you which pages are in the Main Web Index and which pages are in the Supplemental Index.

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