A reference set (or 'refset') is a mechanism used to refer to a set of SNOMED CT components and to add customized information to these components. Reference sets can be used for many different purposes, including representing subsets of concepts, descriptions or relationships, language and dialect preferences, maps to and from other code systems, ordered lists, navigation hierarchies and aggregation hierarchies. For more information about the different types of reference sets, please refer to the  Reference Set Release Files Specification.

Reference sets are used for a range of analytics purposes, including:

• Representing subsets of SNOMED CT concepts with which query criteria are defined and clinical records are matched;
• To represent non-standard aggregations of concepts for specific use cases;
• To define maps from other code systems to SNOMED CT so that clinical data can be prepared for analytics to be performed using SNOMED CT;
• To define language or dialect specific sets of descriptions over which lexical searches can be performed.