Modal window?

hello guys,

i don’t know the exact name for a window that needs an “Ok-click” or “Cancel-click” before you can work further with other windows.

On , if you click “about” or “contact” or “register” you will get a window and the rest of the window will be darker and you can’t click on it.
How is this done???

Is the window a movieclip or a window-component?