Machine learning versus AI: what's the difference?

Thanks to the likes of Google, Amazon, and Facebook, the terms artificial intelligence (AI) and machine learning have become much more widespread than ever before. They are often used interchangeably and promise all sorts from smarter home appliances to robots taking our jobs. But while AI and machine learning are very much related, they are not quite the same thing. Apple is uncharacteristically opening up its artificial intelligence, but how smart is it? Apple is uncharacteristically opening up its artificial intelligence, but how smart is it?