Which of the following best describes "open-source" software?

Open-source software is defined by its availability to the public for modification and sharing due to the accessibility of its source code. This characteristic encourages collaboration and innovation within the software development community, allowing individuals to not only use the software freely but also to adapt it to their specific needs. By being able to modify the source code, users can contribute improvements, fix bugs, and enhance features, promoting a culture of community-driven development.

The other options do not accurately encompass the principles of open-source software. For instance, software that is free to use but not to modify does not align with the open-source philosophy, which emphasizes the importance of user rights to modify software. Similarly, asserting that software can only be used in a commercial environment contradicts the open-source model, which is often associated with community use and non-commercial projects. Lastly, requiring a subscription to use indicates proprietary software, which fundamentally differs from open-source software's core principles of freedom in usage, modification, and distribution.