Application vs. Root

Hi!

Can someone please clearify the relation(s) between Root and Application?
Each Root has exactly one Application?
Why can an application have more than one root objects?

Do those relations have any meaning/impact on window handling?

TIA

Each browser tab, portlet etc. of a single application maps to a Root.

In Vaadin 7, multi-tab support is enabled by default so new Roots are created when navigating to the application on different browser tabs etc.