How is the name of this feature?

I wanna have, when a user clicks an button, the screen should go black and in the middle should be a new webpage.

I know this is very often used for Images, but I know it is possible with webpages too.

How is the name of this feature an开发者_JS百科d how I can get it for my asp.net page?

Are you talking about a "Lightbox" effect ?

http://line25.com/articles/rounding-up-the-top-10-jquery-lightbox-scripts

Modal window

ASP.NET AJAX Toolkit has the ModalPopup control,

Or can use many jquery plugins (ThickBox for example).