Yeah. "header only" had really caught on because it is a catchy term that is simple to understand.

But, what I really, really wish caught on would be "single cpp file" with the expectation that you are capable of adding a single, self-contained source file to whatever build system you happen to be using.

That's often what "header only" libraries really are -- you create your own .cpp file, define a particular preprocessor symbol, and then include the header which will then produce the implementation in that translation unit. Without the symbol defined you only get the interface, suitable for including in other translation units.