What is the meaning of Clustering?

A grouping of a number of similar things.

The grouping of a population based on ethnicity, economics or religion.

The undesirable contiguous grouping of elements in a hash table.

A prewriting technique consisting of writing ideas down on a sheet of paper around a central idea within a circle, with the related ideas radially joined to the circle using rays.

Forming a cluster.

present participle and gerund of cluster

Source: wiktionary.org