A search engine is a program that operates on the Web or within a website searching for specified information. Some rating services indicate that there are about 100 general Internet search engines that are most-used . Others indicate that there are about 300. If you are planning to register a website with search engines, you only need to concern yourself with about 300. Beyond that you are sure to be dealing with those that have a main purpose to collect email or website addresses for redistribution.
Most search engines are specialized or limited as applications by their owners.
Some operate with web robots, which are also called spiders or crawlers. Computers programmed as robots constantly search the web for information that can be feed into their owners' databases and recalled by the use of keywords or phrases. All search engines are biased in different ways. Listings and positionings in these databases are usually paid for. The 15 search engines the Network provides access to are the ones that we know come closest to being non-biased.