IBM's Watson is everywhere lately--but what is it?

Since winning Jeopardy! in 2011, IBM's Watson has apparently found employment as a dress designer, a chef, and a movie director. The latest news is that IBM is doing deals with GM, Slack, and Pearson that will see Watson helping, respectively, with roadside assistance, business messaging, and education. Even if you follow developments in AI closely, though, it can be hard to keep track of all the things Watson can do. It raises a question: what is it, exactly? TV ads that portray Watson as some sort of super-smart Siri don't exactly help.