Aqua

From Mac Guides

Aqua is the name of the graphical user interface (GUI) in Mac OS X, which replaces the Platinum theme of Mac OS 8 and 9. It uses effects such as transparency and reflections, and many of its interface controls (such as buttons and scrollbars) are droplet-like. Aqua also includes interface aspects such as the Dock.

The use of some effects has been toned down in successive releases of Mac OS X, for example transparency is much less common or less obvious in later releases, and the use of pinstripes in window backgrounds is subtler (it has also been completely removed from the menu bar). However, some other effects, particularly those involving animations, are becoming more common. For example, a rotation effect was added in Panther when using fast user switching, and in Tiger the Dashboard uses a ripple effect on Core Image capable machines.

The graphics used in Aqua are powered by Quartz Compositor.

Under Mac OS X Leopard Aqua and the Graphite look have been replaced by a new unified look, similar to the look of Mail under Mac OS X Tiger.