9.1 Clustering

Clustering is an unsupervised learning technique that automatically groups data points so that items in the same group (cluster) are more similar to each other than to items in other groups. Crucially, there are no labels — the algorithm discovers structure on its own based only on the features of the data.

Imagine a telecom company with millions of subscribers but no idea how to group them. Clustering can automatically separate them into groups like heavy data users, voice-only callers, and weekend users — without anyone labelling the customers in advance.