> 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/e/expression.md).

# expression

## expression

**This is an abbreviation for SNOMED CT expression.**

## SNOMED CT expression

A structured combination of one or more concept identifiers that represents an idea.

#### Notes

* An *expression* containing a single concept identifier is referred to as a precoordinated expression. An *expression* that contains two or more concept identifiers is a postcoordinated expression.
* The syntax used to represent *SNOMED CT expressions* is called the SNOMED CT compositional grammar and is formally defined in the Compositional Grammar - Specification and Guide.
* The concept identifiers in a postcoordinated expression are related to one another in accordance with rules expressed in the SNOMED CT Concept Model. These rules allow an *expression* to refine the meaning of a concept by applying more specific values to particular attributes of a more general concept.

#### Example

* The *expression* 284196006:363698007=770850006 represents a burn to the skin of the left index finger.
* An *expression* can also include the terms related to each of the identified concepts as shown below:

[284196006 |burn of skin|](http://snomed.info/id/284196006) : [363698007 |finding site|](http://snomed.info/id/363698007) = [770850006 |Skin structure of left index finger|](http://snomed.info/id/770850006)

## Alternatives

* **Expression**

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