the smallest quantity of some physical property, such as energy, that a system can possess according to the quantum theoryb. a particle with such a unit of energy2. amount or quantity, esp a specific amount3. (often used with a negative) the least possible amount that can suffice: there is not a quantum of evidence for your accusation.4. something that can be quantified or measured5. (modifier) loosely, sudden, spectacular, or vitally important: a quantum improvement.

in physics quantum (plural: quanta) is the lowest amount of any physical entity
involved in any interaction
quanta comes from the word quanta meaning how much

litreally meaning  smallest amount of many forms of energy