> ## Documentation Index
> Fetch the complete documentation index at: https://docs.metriport.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Identifier

> Base StructureDefinition for Identifier Type: An identifier - identifies some entity uniquely and unambiguously. Typically this is used for business identifiers.

## Properties

| Name | Required | Type | Description |
| - | - | - | - |
| id | No | string | Unique id for inter-element referencing |
| extension | No | [Extension](/medical-api/fhir/data-types/extension)\[] | Additional content defined by implementations |
| use | No | code | usual / official / temp / secondary / old (If known) |
| type | No | [CodeableConcept](/medical-api/fhir/data-types/codeableconcept) | Description of identifier |
| system | No | uri | The namespace for the identifier value |
| value | No | string | The value that is unique |
| period | No | [Period](/medical-api/fhir/data-types/period) | Time period when id is/was valid for use |
| assigner | No | Reference\<[Organization](/medical-api/fhir/resources/organization)> | Organization that issued id (may be just text) |


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