OS is an open-source operating system
LINUX and Unix OS is open-source operating system.....! but Windows version OS is not the open-source operating system....!
Classic Mac OS is closed source. Mac OS X is closed source as well, but many libraries and applications within it are open source, e.g. XNU the kernel is open source, and Darwin the underlying UNIX operating system was open source.
Yes it is!
Having the source code open for anyone to edit or modify for free.
The Darwin kernel of Mac OS X is open source, as are many other parts of the OS. (See links below) but Mac OS X itself is not open source and Apple only allows it to run on Apple hardware.
There are many open-source OS distributions (distros) branching out from the Linux Kernel. Ubuntu, Linux Mint, Puppy, to name but three.
Is MacOS an open source system? No.
Meaning of open source OS
Android has been an open source OS since 2008.
In a word... No. Linux is however, which is close to OS X, but is you wanted the source code from Apple, you aren't going to get very far.
An Open Source Database is a list of software that an be used by users who have an open source OS like Linux or Unix. It is mostly free. Anyone has access.