Spaces

Spaces is a feature of Mac OS X that was introduced in October 2007 with Mac OS X 10.5 to let users run up to sixteen virtual desktops to organize their screen real estate.

Usage
Spaces can be triggered via a Hot Corners setting and becomes full screen when opened. The system preferences stay the same on each virtual desktop. However, windows can be moved between desktops. Error messages cannot be moved between virtual desktops, but are otherwise treated as normal windows and stay in the same desktop.

Replacement
With the release of Mac OS X 10.7 in July 2011, it was replaced by Mission Control, which combined Spaces with Exposé.