Earlier, the Software world was rigidly divided between closed and open-source software. Microsoft Windows is closed-source, GNU/Linux is open-source. Microsoft Office and Lotus Notes are closed-source, LibreOffice is open-source. Turbo C++ is closed-source, and GCC is open-source.
But now, a new class of software products has emerged whose core is open-source, but still, the open-source software is of limited use. One model is to offer some critical and useful functionality in a closed-source layer via a managed service in AWS/GCP/Azure, for example, Redis is open-source, but useful modules on top of it are not . Another model is to use licensing gimmickry, for example, MongoDB is licensed under SSPL which requires that if anyone offers MongoDB as a service, then the source code of the full service must be published under this license. The third approach is to make the core software open-source but make it dependent on closed-source cloud services. For example, the node package manager (npm) is open-source, but a closed source company owns the default npm registry. Android is open-source, but most day-to-day application ranging from Google Maps to Google Music are closed-source . Now onwards, rather than calling such software open-source, we should call them closeum.