Unsupervised learning

Learning with nothing labelled. You hand over raw data and the system finds the groupings on its own.

Use it when you do not know what you are looking for. Which customers behave alike, where the natural segments in a dataset fall, which transactions sit outside every normal pattern. It answers the question you would not have known to ask, and what it produces still needs a person to interpret, because the system finds structure without knowing what the structure means.