Explainer: What is deep learning?

Deep learning enables programs to train themselves to understand images and speech. — AFP Relaxnews

Deep learning, a technology based on artificial neural networks, has revolutionised artificial intelligence in the space of a few years. But what exactly is it?

Used by Siri, Cortana and Google Now to understand speech and recognise faces, deep learning is often confused with the concept of artificial intelligence (AI), so much so that the two terms are thought to be synonymous. However, this isn't the case at all. Deep learning is a branch of machine learning, which in turn is a subset of AI. Here's how it works.