Clustering meaning : To form a cluster or group. To collect into clusters. To cover with clusters. The action of the verb to cluster. A grouping of a number of similar things. (demographics) The grouping of a population based on ethnicity, economics or religion. The undesirable contiguous grouping of elements in a hash table. (writing) 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.