Being one of the recurring themes of science fiction, we all have at least a vague idea of what Artificial Intelligence (AI) is. In countless novels and movies, often in the guise of an ominous and threatening machine, other times instead portrayed as a technology so futuristic as to seem almost unattainable, AI has risen to the role of a mysterious entity that mostly belongs to fiction. At least, this was the scenario a few years ago. More recently, in fact, we all came to know AI by witnessing its expansion and pervasiveness to a point where it constitutes a substantial part of our daily interactions, either via smart assistants (e.g., Amazon's Alexa or Apple's Siri, just to name a few), or even by the AI-powered features of our smartphones (e.g., facial and fingerprint screen unlocking, or photo enrichment), not to mention self-driving cars. However, despite being already deployed in millions of products and services around the world, AI is still something obscure.