I’ve had some good conversations about this attempt to define proprietary software. In many of these conversations, people focused on explicitly what I’m trying to not do (i.e. define “proprietary” by saying it’s not FOSS). Some people helped me clarify that I’m looking to do really, which is have a pithy way to explain proprietary to people who are never going to look at source code or pay someone to write new code for them. How do you explain to people who don’t care about technical matters nor have the language to discuss them? How do you talk about licenses to people who may not have the language for it? (In a past life I explained Creative Commons licenses to academics and educators.)
Talking about licensing seemed very important to people, as licenses are what define freedoms, restrictions, and restrictions that protect freedoms. With these points in mind, I present the following:
Proprietary software is software that comes with restrictions that retain control of how software can be used, shared, and changed through the use of copyright and licensing.
I worry that this is “too technical” and then I worry that I’m worrying too much about that. In this I added a truncated version of a common explanation of the Four Freedoms (typically use, study, modify, share). This is in part because I believe “study” is included in “modify.”
I included “copyright and licensing” in hopes that a reader would understand at least one of them. I also wanted to take into account that communities may have other policies (e.g. community guidelines) that might in some way restrict how software is used, shared, and changed. I don’t like “retain control” as a phrase, but it was suggested to me (thanks! If you want credit, just ping me). I think it’s pretty clear about the intention and consequence of proprietary licensing.
A potential criticism I see is that it’s not clear enough that you must be able to do all three (use, share, and change) in order for software to be FOSS and that restrictions on any of them renders software proprietary.