> ## 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)       |