What is Clustering?

Clustering definition and meaning on Dictionary terms:
a number of things of the same kind, growing or held together; a bunch: a cluster of grapes.
a group of things or persons close together: There was a cluster of tourists at the gate.
U.S. Army. a small metal design placed on a ribbon representing an awarded medal to indicate that the same medal has been awarded again: oak-leaf cluster.

Phonetics. a succession of two or more contiguous consonants in an utterance, as the str- cluster of strap.
Astronomy. a group of neighboring stars, held together by mutual gravitation, that have essentially the same age and composition and thus supposedly a common origin.Compare globular cluster, open cluster, stellar association.

verb (used with object)
to gather into a cluster or clusters.
to furnish or cover with clusters.

verb (used without object)
to form a cluster or clusters: The people clustered around to watch.