For practical reasons, a reference set needs to be identified and named, so it can be referred to unambiguously. In a reference set, the reference set is identified by the refsetId attribute, which refers to a concept.
This concept is a subtype of the concept 900000000000455006 |Reference set (foundation metadata concept)|.
As for other all concepts in SNOMED CT, descriptions and relationships are are added to enable human-readable representation of the concept, and to place the concept in the SNOMED CT hierarchy. The descriptions provide the name of the reference set, and the relationship refers to the concept representing the reference set type. This is illustrated in the diagram below where the concept with the id 49999999102 has the associated description "Infectious disease simple reference set", and the relationship places the concept as a subtype of the concept 446609009 |Simple type reference set (foundation metadata concept)|.
Figure 4.2.1-1: Reference sets are identified by SNOMED CT concepts