The phrase comes from AI research, where it names a system that improves the process that improves it. Labs use it for models that help build their successors. In operations it means something smaller and more useful: the system around the model changes, run after run, while the model's weights stay as they are.
Three parts make a loop recursive rather than a one-off fix. Something records numbers from real runs. Something reads them and changes how the work is done: a step, an instruction, a model choice, a schedule. And the next runs are measured against the same numbers, so each change becomes the input to the next decision. When the workflow that makes the changes is measured the same way, it can be improved by the same loop.
The hard part is the ruler. A loop that may redefine its own metric or move its own target learns to pass, not to get better, and the research on self-improving agents records exactly that. A loop that works keeps three things with people: what each metric means, what the target is, and what the loop is allowed to change.