> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-international-documents/snomed-ct-glossary/s/subset.md).

# subset

## subset

A set of members all of which are members of another set (from *set theory* in mathematics).

#### Notes

* In SNOMED CT, the definition of *subset* applies to SNOMED CT components as follows:
  * A subset of SNOMED CT concepts is a set of concepts taken from a wider set of concepts.
  * A subset of SNOMED CT descriptions is a set of descriptions taken from a wider set of descriptions.
* The members of a subset can be defined in one of two ways:
  * Extensionally, by enumeration, with a simple reference set as the standard distribution format.
  * Intensionally, using rules to determine inclusion, with a query reference set as the standard distribution format.

#### Examples

* A subset of SNOMED CT concepts from all of the concepts in a particular version of a SNOMED CT edition.
* A subset of SNOMED CT descriptions from all the descriptions in a particular version of a SNOMED CT edition.

## Related Links

* Wikipedia
  * [Subset](https://en.wikipedia.org/wiki/Subset)

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