What is Search Engine

Search Engine is online database contain diffrent type of information related to all over world.where we find the information use of specified keywords and returns the list of documents.it has some component
1. search engine software
2.spider software
3.relevancy algorithim
there are alot of search engine used in the internet some are most ly used by user like
1.Google
2.MSN
3.Yahoo
4.Altavista