A Massive-Context Clozed Deletion cards (shortened to MCD) is basically a paragraph in the target language cut-and-pasted into a flash card program (like Anki). Multiple words in the paragraph are "clozed", i.e. they are hidden so you'll have to guess their meaning. The term was popularized by the All Japanese All The Time blog. As native materials are required, MCDs work best for intermediate learners (although mini or micro-MCDs are also possible, and you can even use MCDs to practice grammar).