The terms "supervised machine learning" and "unsupervised machine learning", by their ordinary English meaning, make it sound like all machine learning is partitioned into one or the other. But a lot of the literature in machine learning considers reinforcement learning to be neither 'supervised learning' nor 'unsupervised learning'. See, e.g., section 1.1 of [1].
[1] Richard Sutton and Andrew Barto, Reinforcement Learning: An Introduction, second edition. MIT press, 2018.
