Programmatic interface for interacting with components. In Kubernetes this might be the kube-apiserver, and in Flux it could be a socket (connected via flux proxy) or the flux restful API.
Converged Computing Authors. "Application Programming Interface." Converged Computing Community Space 21 May 2025, https://converged-computing.org/docs/application-programming-interface/ (accessed 21 May 25). [doi]