The 'cluster' concept describes DNA fragments containing several genomic "entity" instances.
The definition of a cluster describes the instances which are present in the sequence but not their number.
For instance, the V-(V-D-J)-CLUSTER comprises two kinds of entities : V-GENE and V-D-J-GENE. The 'cluster' concept allows to describe a set of genes in a locus. There are fourty instances for the 'cluster' concept. Definitions of these instances are available in the IMGT standardized labels.
The 'cluster' concept is part of the 'DESCRIPTION' concept of IMGT-ONTOLOGY .
Reference:  Giudicelli, V. and Lefranc, M.-P., Bioinformatics, 15, 1047-1054 (1999) PMID: 10745995, LIGM:221