This is the "http-based remote procedure calls" usage of the term API, and not the "function call definitions for a programming language" usage of the term API.

This is the "http-based remote procedure calls" usage of the term API, and not the "function call definitions for a programming language" usage of the term API. (Yes, at some level they are conceptually the same thing. But it's worth pointing out due to the already-mentioned confusion with OpenCV, and for those of us that got confused in the early 2000s when a common terminology for C/C++/Java libraries suddenly started to mean "web-hosted software as a service", and still haven't fully recovered.)