It's just the naming scheme that Apple has adopted for its Mac OS release.
It's a reflection of what impression they want to give regarding the OS itself. You may notice though they use the "Big Cats" name for their OS. They tend to use names of animals in this genus that are capable of roaring.
Cats. 10.0, Cheetah 10.1, Puma 10.2, Jaguar 10.3, Panther 10.4, Tiger 10.5, Leopard 10.6, Snow Leopard
Each version of Apple's Mac OS X is named after a big cat. Mac OS X 10.5 is called "Leopard".
Mac OS X is an operating system released by Apple Inc. It is designed for Apple branded computers, which is why you will never see a Dell, or an HP computer run Mac OS X. There are only two important versions of Mac OS X, Mac OS X Server, and regular Mac OS X. Mac OS X server was designed for servers, while regular Mac OS X was designed for most computers. The current version of Mac OS X (10.6) is named Snow Leopard.
Mac OS X Mountain Lion is currently the newest operating system released by Apple, Inc. and is equivalent to OS X version 10.8. All of the Mac operating systems beginning with version 10 (X) have had codenames that are named after large cats, beginning with 10.0, Cheetah. The name of the "cat" changes depending on the number after the 10, e.g. 10.1 was codenamed "Puma," while 10.2 was known as "Jaguar." Jaguar was the first of the OS X releases to have its internal codename as part of its public branding.
Mac OS X Mountain Lion is currently the newest operating system released by Apple, Inc. and is equivalent to OS X version 10.8. All of the Mac operating systems beginning with version 10 (X) have had codenames that are named after large cats, beginning with 10.0, Cheetah. The name of the "cat" changes depending on the number after the 10, e.g. 10.1 was codenamed "Puma," while 10.2 was known as "Jaguar." Jaguar was the first of the OS X releases to have its internal codename as part of its public branding.
Apple's Mac OS X. OS X Lion OS X Panther OS X Leopard etc.
I have a Mac OS X but I know Mac OS is a computer made by the brand/company, Apple.
You cannot without erasing your hard drive and installing Mac OS 9 from scratch. Even then Mac OS 9 may not run on modern Mac hardware because Mac OS 9 needs the ROM chip to boot. Modern Mac OS X hardware uses EFI to boot the system instead of a ROM chip to boot. Mac OS X v10.0 - Mac OS X v10.4 support Mac OS 9 applications and can run them, you just need to install the Mac OS 9 compatibility program which can be found on the Mac OS X Install CD.
The second name of Mac OS X v10.4.5 is Mac OS X v10.4 Intel.Mac OS X 10.4 was known as Mac OS X Tiger.
Each version of Apple's operating system for their computers, Mac OS X, is named after a member of the cat family, Tiger, Panther, Leopard etc. The current version, Mac OS X 10.6, is known as Snow Leopard.
Mac OS Leopard
The oldest mac OS is System 1