A mental cycle is an arbitrary unit of “mental computing power” that is used to measure the mental costs of performing certain tasks. You can say finding the square root of 81 requires fewer cycles than finding the square root of 5329. You can say a smart person has a lot of mental cycles, which means that they can think a lot. You can also say that a smart person uses their mental cycles very effectively, meaning that even if they’re slow, they have good heuristics around how to solve problems efficiently. Students who spend 10 minutes on a test that should have taken 60 are either geniuses or cheating. Teachers intuit possible explanations to quick test turnaround times with the implicit concept of mental cycles.