A MOOC (say it like “mook”) is a massive open online course: a course on the internet that a very large number of people can take, often for free or for little money. Massive means thousands of students at once; open means, in principle, anyone may join; online means it lives on the web; course means there are lessons, not just a random video. Universities and companies put up a wave of these in the early 2010s. You take a MOOC, sign up for a MOOC, finish a MOOC. People still sometimes say the letters M-O-O-C, but the usual pronunciation is one syllable. Though actually, “open” is used a bit loosely: some MOOCs are free to watch but charge you for a certificate.