In a lot of logging systems, debug is one of the common levels of logging. I'm not even convinced that the term "debug" is unambiguous to clearly refer to something that's not a subset logging. Presumably the difference is intended to mean things printed that are unconditionally going to stdout rather than into some system that might change the output location and filter/annotate things, but I have to imagine that it might just make more sense not to have separate models for them at all