https://akilian.com/2019/12/30/worker-in-the-loop-retrospective

A service is considered human-in-the-loop if it organizes its workflows with the intent to introduce models or heuristics that learn from the work of the humans executing the workflows. In this post, I will make reference to two common forms of human-in-the-loop:
• User-in-the-loop (UITL): The end-user is interacting with suggestions from a software heuristic/ML system.
• Worker-in-the-loop (WITL): A worker is paid to monitor suggestions from a software heuristic/ML system developed by the same company that pays the worker, but for the ultimate benefit of an end-user.