Comment by zabzonk

I would say that systems programming is writing software to support users of a system - those using the operating system. The same users might also be using application software - say an accounting package. Maybe the application software interacts with particular systems software, maybe not.

The implementation language doesn't matter. An example of a systems program is a distributed printer spooling program I wrote in ReXX on VM/CMS in the mid 80s. All of our VM/CMS users used it, because it was far more convenient than IBM's offering, and supported our pre-existing line printers and the physically distributed nature of our organisation.