are handy tools that help you find what you want on the Web.
engine uses software (called spiders or robots) to compile a database
of pages found on the publicly accessible Web. When you enter a
search, the search engine scans its own database to match your terms
against terms in the pages of its database.
So, each search
engine searches the part of the Web it has collected -- not the
whole Web -- and each search engine has a somewhat different database.