From the Yahoo UI Blog:
This principle captures the idea that every piece of logical content does not have to be on a different page. Instead when we design a content page, especially a home page, we should consider how we can expand the user’s virtual space. In many ways this is similar to creating a play. At any given time the view on the stage is only a small part of the action. The backstage, props, and other actors are all being prepared for the next scene. A home page can provide ways to allow a user to take a “sneak peek” at additional content and essentially “open up” the page space.
This is just what the new Yahoo! home page has done.