What is an open-source operating system?

Open-source means that you can get the source code of the software for free (source code is the code of the program written in a certain programing language). Operating system is the software that you use to operate your PC (like Windows or Linux)

Operating system can be any Linux or UNIX flavour, but important thing is File system. ZFS is best suite for storage, so snapshot, writable clone and replication is free. Most of the storage company used to charge too much money as snapshop/clone and replication license.

ZFS is very simple and convenient. You can use any operating system under vmware or Virtual box that support ZFS so you can manage your logical devices on top of physical devices. You don't need to purchase any hardware or software to manage your storage.
OS means operating system, which is the computer programming that 'operates' a computer. Open source refers to any application for which you can see and change the underlying code. A big advantage of an open source program is that it is a collaborative between many people. If there is a problem, many people will see the problem and work on a solution. Linux is an example of an open source operating system. Windows and Macintosh both are closed (proprietary) systems.