quantum [M16] Although you will often come across a sentence like ‘This product represents a quantum leap forward’, the curious thing about the term quantum leap [M20th] is that, strictly speaking, it does not describe a large change at all, but a tiny one. Quantum comes from Latin quantus, ‘how big?’ or ‘how much?’, and originally meant ‘a quantity or amount’. In physics a quantum (a term introduced by the physicist Max Planck around 1900) is a very small amount of energy, the minimum amount of energy that can exist in a given situation, and a quantum jump [E20th] is the abrupt change of an electron or atom from one energy state to another. Although this is a tiny jump in terms of size, it is an instantaneous and dramatic one, which explains why the term came into general usage from around 1970 to describe a sudden large increase or major advance. Quantity [ME] comes from the same root as quantum.