What Is an API and Why Does It Matter?

The API or application programming interface is becoming the interface for business. In much the same way that storefronts gave way to applications and websites, argues a16z general partner Martin Casado, we’re now seeing more and more companies whose primary interface is a set of programmatic functions offered as a service. But what is an API? How do they work? And from the automobile to the computer, why does the API represent a key evolution in and beyond the computing industry?
credits: historical footage courtesy of Prelinger Archives; music "Breezin" by Podington Bear; all trademarks are the property of their respective owners