KB User's Guide - API - What is an API?
A quick look at API use in the KB
An Application Program Interface (API) is a set of routines, protocols, and tools for building software applications which specifies how software components should interact. They essentially provide a means to receive and/or send data to and from an application. Because the data is stripped of information related to its presentation, it can more easily be consumed by other applications.
For more background the KB's APIs, you can watch the recording of KB Architect, Weizhong Wang presentation at the 2016 KB User's Group Meeting; the specific section relating to APIs starts at 12:24 in the recording: https://uwmadison.box.com/s/n5248ahuczdd7i8y3ns6wze4zjdtgxqk
For a more in-depth explanation of how APIs work, please read the following article: https://medium.freecodecamp.com/what-is-an-api-in-english-please-b880a3214a82