Clustering is the process of grouping data objects into a set of disjoint classes, called clusters, so that objects within a cluster have high

similarity to each other, while objects in other clusters are more dissimilar. Clustering is an example of unsupervised classification.

"Classification" refers to a procedure that assigns data objects to a set of predefined classes. "Unsupervised" means that clustering does not rely on predefined classes and training examples while classifying the data objects.