Answer:
Umm... Yes. But I'm talking about Mac OS X. If you want to run Mac OS Classic, well, sorry. You need another piece of software to emulate the environment, but if you have Mac OS X 10.3 or 10.4, you can run Classic Mode on it, but you would need a Mac OS Classic Installation CD
__Mac OS__ is basically like Windows 95, Windows 98, Windows ME, etc, is to "Windows" today, it just refers to ANY Macintosh operating system in general.
They have just made the phrase _MAC OS_ easier to distinguish between software that works on a Windows machine or a Mac and to show the software is made for the Mac only.
Usually in the description it will give the actual parameters of how old the software will work, PowerPC or Intel Macs or OS 9, 10.2, 10.3, etc.
OS-X refers to OS-10.1.x all the way to 10.6.6 as of today.
OS-9 will only "boot" on older PowerPC machine's and "Classic" is an emulator in OS-X and will run "Most" of the OS-9 software on the "newer" Mac OS-X (10.1 to 10-4) "Classic" ended at OS-10.5.