In quantum mechanics, quanta (singular: quantum) are the minimum amounts of any physical entity involved in an interaction. For example the minimum energy of a photon is defined by the planck constant and it’s wavelength. The origin of the photon could be high energy but it still ends up being a ‘packet’ that can then interact with another particle like an electron cloud which can move electrons around.
The fundamental notion is that a physical property may be "quantized," referred to as "the hypothesis of quantisation". This means that the magnitude can take on only certain discrete values.
A photon is a single quantum of visible light as well as all other forms of electromagnetic radiation and can be referred to as a "light quantum". The energy of an electron bound to an atom is quantized, which results in the stability of atoms, and hence of matter in general.
As incorporated into the theory of quantum mechanics, this is regarded by physicists as part of the fundamental framework for understanding and describing nature.
source adapted from: Quantum. (2015, December 5). In Wikipedia, The Free Encyclopedia. Retrieved 06:40, January 14, 2016, from https://en.wikipedia.org/w/index.php?title=Quantum&oldid=693853902