What distinguishes open-source software from proprietary software?

The characteristic that distinguishes open-source software from proprietary software is that it allows users to view and modify the source code. This openness invites collaboration and encourages a community of developers to innovate and improve upon the software. Users can adapt the software to their own needs, fix bugs, and share their modifications with others. This is in stark contrast to proprietary software, where the source code is kept secret, and users are typically limited to using the software as-is without permission to alter it.

While it is true that many open-source software programs are available for free, it is not a requirement, as some open-source software may have associated costs for distribution or support. The notion that open-source software lacks a user interface is also incorrect because many open-source programs have well-designed user interfaces. Furthermore, open-source software is not restricted to educational purposes; it can be used in various contexts, including commercial use, which broadens its applicability. Thus, the ability for users to view and modify the source code is the hallmark feature of open-source software.