In physics, a quantum (PL: quanta ) is the minimum amount of any
physical entity (physical property) involved in an interaction.
The fundamental notion that a physical property can be "quantized" is referred
to as "the hypothesis of quantization". This means that the magnitude of the
physical property can take on only discrete values consisting of integer
multiples of one quantum. For example, a photon is a single quantum of light
of a specific frequency (or of any other form of electromagnetic radiation).
Similarly, the energy of an electron bound within an atom is quantized and can
exist only in certain discrete values. (Atoms and matter in general are stable
because electrons can exist only at discrete energy levels within an atom.