Machine learning is the branch of AI where systems learn patterns from data instead of following explicit rules. You show examples; the system adjusts internal parameters until its outputs match the examples — then it generalizes to new cases.
ML is the practical core of modern AI. It explains why data quality decides model quality — and why a system can fail exactly where its training data was thin.
A spam filter learns from millions of labeled emails; it never reads a rule saying 'FREE MONEY = spam', it infers the pattern itself.