Hiding an application, very simply and straightforwardly, just takes the application out of the foreground and makes all its windows disappear. They are still considered to "exist", in the same desktops/spaces, and no state is lost—when you switch back to the application, all its windows reappear exactly as they were when you hid it (assuming no background processing changed them, of course). They are just not visible for as long as you keep the application hidden.
The difference between this and minimizing is that a) it affects all windows of the application, not just a selected one, and b) a minimized window either goes into the side of the Dock, or into the application icon on the Dock (depending on your set preferences); hidden windows, as I said, are completely invisible.
There is also a "Show All" option under the application menu (the one just to the right of the Apple menu, with the name of the foreground application) that will un-hide all currently hidden applications.
Virtual desktops are a relatively recent addition to the Mac; this hiding behavior has been around and worked consistently since the mid-'90s, well before Mac OS X.
(As a final random tidbit, one of my most common methods of hiding an application—particularly if it's the one I'm using at the time—is to simply option-click on either the desktop or another application's window, as that is a longstanding shortcut for doing so.)
The difference between this and minimizing is that a) it affects all windows of the application, not just a selected one, and b) a minimized window either goes into the side of the Dock, or into the application icon on the Dock (depending on your set preferences); hidden windows, as I said, are completely invisible.
There is also a "Show All" option under the application menu (the one just to the right of the Apple menu, with the name of the foreground application) that will un-hide all currently hidden applications.
Virtual desktops are a relatively recent addition to the Mac; this hiding behavior has been around and worked consistently since the mid-'90s, well before Mac OS X.
(As a final random tidbit, one of my most common methods of hiding an application—particularly if it's the one I'm using at the time—is to simply option-click on either the desktop or another application's window, as that is a longstanding shortcut for doing so.)