Reference
Concise definitions of FHIR and healthcare interoperability concepts. Reference answers what is this — for how to use it, see Learn.
Core Concepts
FHIR
HL7 standard for exchanging healthcare information over REST APIs.
See also: Resource, REST API
Resource
The fundamental unit of FHIR — a structured JSON document with a defined schema.
See also: FHIR, Bundle
REST API
The HTTP interface for interacting with FHIR resources using standard verbs and URL patterns.
See also: FHIR, Search
Search
The FHIR query mechanism for finding resources using URL parameters.
See also: REST API, Bundle
Bundle
A container for multiple FHIR resources — used for transactions, search results, and documents.
See also: Resource, Search
CapabilityStatement
A machine-readable description of what a FHIR server supports.
See also: REST API, Profile
OperationOutcome
The standard FHIR resource for returning errors, warnings, and informational messages.
See also: Validation, REST API
FHIRPath
A path-based expression language for navigating FHIR resources, used in profiles and search.
See also: Profile, Slicing
Clinical Resources
Patient
Demographic and administrative information about a person receiving care.
See also: Observation, Encounter
Observation
A measurement or assertion about a patient — vital signs, lab results, clinical findings.
See also: Patient, Condition
Condition
A clinical finding, diagnosis, or complaint assessed by a clinician.
See also: Patient, Encounter
Encounter
An interaction between a patient and healthcare provider — a visit, admission, or telehealth call.
See also: Patient, Condition
MedicationRequest
A prescription or order for a medication — drug, dose, route, frequency.
See also: Patient, Encounter
Profiling & Conformance
Profile
A StructureDefinition that constrains a base resource for a specific use case.
See also: StructureDefinition, Validation
StructureDefinition
The FHIR resource that defines the structure of other resources, profiles, and extensions.
See also: Profile, Extension
Extension
Adds a data element to a resource that is not part of the base FHIR specification.
See also: StructureDefinition, Profile
Must-Support
A profile flag requiring systems to store and return an element if present.
See also: Profile, Implementation Guide
Slicing
Splits a repeating element into named sub-types with their own cardinality and constraints.
See also: Profile, Extension
Implementation Guide
A publishable specification bundling profiles, value sets, examples, and conformance rules.
See also: Profile, ValueSet
Validation
Checking that a resource conforms to the FHIR specification or a profile.
See also: Profile, OperationOutcome