What is the Apple desktop called?

It depends on what you mean by "desktop".

If you are referring to a "desktop computer", Apple makes two. The more popular consumer-friendly one is called the "iMac". The pricier, more professional version is called the "Mac Pro". Apple created a revolutionary new design for their Mac Pro in 2013.

If you are talking about the Mac OS X interface then the desktop is actually called "The Desktop". The term refers to the base screen of the Finder, which is the program used to find and manage files on the Mac. The terms "Finder" and "Desktop" are often incorrectly used interchangeably.