I’ve seen this term pop up in several different places, but I’m having trouble finding reference of what an API Interface is. My assumption is that it is some layer of abstraction between the actual API implementation and the client, but I’m not really sure. I found the term referenced by Google in Google’s Cloud API @ https://cloud.google.com/apis/design/glossary#api_interface
After reading it I’m still not exactly sure what it is. What is it, and why is it useful when designing API’s?