OSX (now macOS) is an operating system that is considered closed source, meaning that its source code is not publicly available or modifiable by anyone except its developers. It is owned and maintained by Apple Inc. Ubuntu, Android and CentOS are operating systems that are considered open source, meaning that their source code is publicly available and modifiable by anyone who wants to contribute or customize them. Verified References: https://www.comptia.org/blog/open-source-vs-closed-source-software https://www.comptia.org/certifications/a