(Finding and visually documenting groups of facts not previously known)
Clustering is a data mining technique that makes meaningful or useful cluster of objects that have similar characteristic using automatic technique.
Different from classification, clustering technique also defines the classes and put objects in them, while in classification objects are assigned into predefined classes.
To make the concept clearer, we can take library as an example.
In a library, books have a wide range of topics available. The challenge is how to keep those books in a way that readers can take several books in a specific topic without hassle.
By using clustering technique, we can keep books that have some kind of similarities in one cluster or one shelf and label it with a meaningful name. If readers want to grab books in a topic, he or she would only go to that shelf instead of looking the whole in the whole library.