To understand is to make connections and bind together our knowledge into something that makes sense of things (whereas without understanding we might see only unclear, isolated, or unhelpful facts). But the word also implies doing, not just a mental act: A performance ability lies at the heart of understanding, as Bloom (1956) noted in his Taxonomy in discussing application and synthesis. To understand is to be able to wisely and effectively use—transfer—what we know, in context; to apply knowledge and skill effectively, in realistic tasks and settings. To have understood means that we show evidence of being able to transfer what we know. When we understand, we have a fluent and fluid grasp, not a rigid, formulaic grasp based only on recall and “plugging in.”