Has this ever happened to you as a manager?
One of your direct reports doesn’t do what their job (function) requires them to do. Perhaps they didn’t get a report in on time or they showed up late for work because they slept in or they left out a crucial step in a project which caused a delay in production.
Each of these behaviors is “non-performance”. In other words, the person who reports to you hasn’t “performed” what’s required of them in their function.
And, as a manager, you’re expected to deal with it.