Types of Search Engines and Web Directories

Many search engines exist on the Internet. How do you make sense out of all the offerings?
The following subsections go into detail regarding several different types and
groups of search engines, including primary, secondary, regional, topical, web spider
(based), meta, and hybrid search engines.

First-Tier Search Engines
Google, Yahoo!, and Bing are considered first-tier, or primary, search engines, as they
own most of the search engine market share in the Western parts of the world. These
search engines usually scour the entire Web, and in the process create very large index
For all intents and purposes (and if you reside in the Western world), primary search
engines are the only ones you should really care about, as most of your visitors will
have come from these search engine sources.

Second-Tier Search Engines
Secondary or second-tier search engines are lesser known or not as popular as first-tier
search engines. They may provide value similar to that of the most popular search
engines, but they simply cannot compete with them, or they may be new. You will
obviously not be spending much of your time optimizing your sites for these types of
search engines.