What is symbolic artificial intelligence?

This article is part of Demystifying AI, a series of posts that (try to) disambiguate the jargon and myths surrounding AI. Today, artificial intelligence is mostly about artificial neural networks and deep learning. But this is not how it always was. In fact, for most of its six-decade history, the field was dominated by symbolic artificial intelligence, also known as "classical AI," "rule-based AI," and "good old-fashioned AI." Symbolic AI involves the explicit embedding of human knowledge and behavior rules into computer programs. The practice showed a lot of promise in the early decades of AI research.