Mac OS X (pronounced "mac oh ess ten") is an operating system developed by Apple Inc. for their line of Macintosh computers. It is the successor to Mac OS 9, which was the previous version of the operating system for Macintosh computers. Mac OS X is based on the Unix operating system and features a user interface that is similar to that of the Macintosh operating system.
The correct way to pronounce Mac OS X is "mac oh ess ten," with each letter pronounced individually. It is not pronounced as "mac os ex" or "mac os ten."
Note that the "X" in Mac OS X does not stand for the Roman numeral "ten," but rather is a reference to the X Window System, which is a component of the Unix operating system and is used to provide a graphical user interface (GUI) for Unix-based systems. The X Window System was originally developed at MIT in the 1980s and is used in many Unix-based operating systems, including Linux.