It was announced that Facebook application pages will now be accessible to the public.
This means that visitors need not be logged in to (or even a member of) Facebook to see the apps description.
It is just the “home” page of the application where the app is described to those who might want to use it. For example here is a canvas page for a Stephen Colbert app I am playing with.
You can see this page even if you are logged out of Facebook. Prior to this announcement, if you followed the same link above, you would have been instructed that you could not see the page until you signed in.
The canvas page itself only changes slightly when a user is not logged in, there is a new button that shows up a couple places on the page to invite people to sign up for Facebook so they can use the application.
There are some technical details here on how to implement this on the wiki.
This means that a Facebook app page can now be marketed much easier, it is a pretty important change to know about.