This morning I was reading a site that regularly covers free and open source software. To protect the guilty party (because I suspect the error was one of rushed writing rather than ignorance), I'll leave out the publication and author. However, I do want to surface the error. The author wrote about making sure that "copyrighted code" doesn't get into the Linux kernel. What?
All (or almost all, there may be some public domain code) of the code in the Linux kernel is under copyright. That's what the GPLv2 is, a license for using copyrighted material.
What the author probably meant was "proprietary" code, not "copyrighted" code. This is an easy error to make, but also a dangerous one.
As we all know, or should, free and open source software depends on copyright just as much as proprietary code. Just because we use the (brillant, IMHO) term "copyleft" to describe some free software, it doesn't mean the code isn't also under copyright. It is, that's why the GPL works, because owners of GPL'ed works can use copyright law to enforce the terms of the license.
Using "copyrighted" as shorthand for "proprietary" makes it easier for FOSS opponents to paint FOSS supporters as "against copyright" entirely. It also promotes a mistaken idea that free software licensing contains no restrictions whatsoever. Neither of those things are desirable.
If you're writing or talking about software licensing and want to convey the difference between free/open source code and proprietary, say "proprietary." Using "copyrighted" is not only in error, it actively undermines FOSS.