Rakib,
Search engine usually have their own database of sites they craw and list in their database, for example Google, Yahoo, Ask.
Meta Search Engines usually do not have their own database of crawled sites, they search the databases of real search engines, usually many search engines at the same time, and provide you results. So a meta search engine will give you results from say Yahoo and Google, some meta search engines do have database of sites submitted to them. Example of a meta search engine is DogPile.

Thanks Temi for prompt reply. Temi, can you guide If I launch a meta search engine, where I can got a quality script & suitable web hosting?

You can find many meta search engine scripts here: Hotscripts.com :: The net's largest PHP, CGI, Perl, JavaScript and ASP script collection and resource web portal or here: The Resource Index Online Network
Thanks

meta tag is useless now.. what search engine want is content.

MxHub, I am not sure I completely agree with you on meta tags being completely useless, it still plays a role