What defines open-source software?

Open-source software is defined by its licensing, which allows users not only to view the source code but also to modify and distribute it. This characteristic promotes collaboration and community contributions, enabling individuals and organizations to improve upon existing software, fix bugs, and tailor applications to their specific needs. The freedom to access the code provides opportunities for innovation and learning that proprietary software typically does not allow.

The other choices suggest limitations that are not in line with the principles of open-source; for instance, being required to purchase software or subscribe for use negates the fundamental concept of accessibility inherent in open-source frameworks. Similarly, software that is free to use but restricts modification goes against the core value of open-source licensing, which emphasizes the ability to adapt and improve shared code.