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API Engineering Glossary

Term Meaning
API contract Documented request, response, error, security, and behavior agreement for an API.
API category Public application, internal, AIOS tool, or integration API grouping.
Application service Modulith service that executes a command or query for a Domain.
Correlation ID Identifier used to trace related requests, commands, events, and logs.
Causation ID Identifier showing which prior request, command, or event caused the current request.
Entitlement Billing-owned access grant, feature right, or usage limit.
Idempotency key Client-provided key used to make unsafe retries safe.
OrganizationId Identifier for the customer organization and organization-scoped resource boundary.
OpenAPI Future source-of-truth format for approved REST API contracts.
Public application API API used by mobile or web app experiences.
Internal API API used by internal services, backend workflows, or AIOS tool calls.
Integration API API boundary for external systems, providers, partners, or callbacks.
Tenant context Context that identifies the tenant boundary and enforces isolation.
Standard envelope Common response wrapper for data, metadata, links, and errors.
Source fact Business fact owned by a Domain module.