This is my favorite article on APIs so far. Most of them only refer to remote APIs as being HTTP requests. This article has a broader scope but also keeps the information simple for up and coming developers.
Awesome article, I must say I did not have solid knowledge of API’s until I saw this. I used to think API’s happen only to the client server type of network whereby a server serves specific responses based on client request. I did not realize it could still mean a set of methods used to interact with an object.