Three types search engines

Crawler-Based Search Engines:

Crawler-based search engines create their listings automatically. They "crawl" or "spider" the web, then people search through what they have found. If anybody changes the web pages, crawler-based search engines ultimately find these changes, and that can affect how you are listed. Page titles, body copy and other elements all are played in a role.

Human-Powered Directories:

Human-powered directory depends on humans for its listings. When you submit a word or short description to the directory for your query the sites review. Search looks for matches only in the descriptions submitted. Changing your web pages has no effect on your listing. Things that are useful for improving a listing with a search engine have nothing to do with improving a listing in a directory. The only exception is that a good site, with good content, might be more likely to get reviewed for free than a poor site.

Hybrid Search Engines or, Mixed Results:

Early days, it’s used to be that a search engine either presented crawler-based results or human-powered listings in the web. Now, it’s extremely common for both types of results to be presented. Usually, a hybrid search engine will favor one type of listings over then another especially for more obscure queries.