As an example, you could describe a spinning disk hard drive as "RAM" because it's a memory device you can randomly access. That would meet the dictionary definitions of "random", "access", and "memory". And yet, everyone would be annoyed with you for doing so. "I have 16TB of RAM in my computer!" "No you don't, Kebab. Stop saying that!"
> Generally, open source refers to a computer program in which the source code is available to the general public for usage, modification from its original design, and publication of their version (fork) back to the community.
As others said, while "open" does indeed mean "reachable" or "available" in this context of source code, it happens that "open source" is a well defined thing to allow not only access, but also modification, reuse, and distribution without limitations. So the "open" in "open source" has its meaning brought to the highest level of openness.