It's not a formally defined spec or standard — it's a design philosophy Kelsey Hightower champions, borrowed from intent-based networking (Cisco, etc.) and applied to APIs and infrastructure.
Kubernetes is the canonical example — you declare desired state, the control loop reconciles reality to match it. You never say "start container on node X, then update the load balancer" — you say "I want 3 replicas of this."
Contrast with imperative APIs: "do this, then that, then handle this error case." Intent-based APIs absorb the operational complexity on the platform side.
For Enterprise Architecture purposes: it's essentially declarative architecture at the API surface — which maps cleanly to DBJ Taxonomy Logical tier. The implementation detail is hidden below. Worth noting it aligns with TOGAF's separation of what (architecture) from how (engineering).
Foundations Software Defined Netowrking (SDN) serves as a foundational element of a comprehensive intent-based networking (IBN) architecture. SDN has been limited to automated provisioning and configuration. IBN now adds "translation" and "assurance" so you can automate the complete network lifecycle and continuously align the network to business needs.