In Mac OS X the Desktop is the area of the screen where your work begins.  After you turn on and log into your Mac you are taken to the desktop.  When there are no open application windows you will see something similar to the following on Mac OS X Tiger.

Mac OS X is capable of presenting to the user various icons.  Icons play a vital role throughout the operating system, in application windows, and within applications (programs).  Icons are simply symbols or graphics used to represent an entity with a particular program, window, or option.

When you preform certain desktop actions Mac OS X will play a short sound that lasts only a fraction of a second.