In physics, a quantum (plural: quanta) is the minimum amount of any physical entity involved in an interaction. Behind this, one finds the fundamental notion that a physical property may be "quantized," referred to as "the hypothesis of quantization". This means that the magnitude can take on only certain discrete values.
A photon is a single quantum of light, and is 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 at the smallest length-scales.
Quantum is the Latin word for amount and, in modern understanding, means the smallest possible discrete unit of any physical property, such as energy or matter . Quantum came into the latter usage in 1900, when the physicist Max Planck used it in a presentation to the German Physical Society. Planck had sought to discover the reason that radiation from a glowing body changes in color from red, to orange, and, finally, to blue as its temperature rises. He found that by making the assumption that radiation existed in discrete units in the same way that matter does, rather than just as a constant electromagnetic wave, as had been formerly assumed, and was therefore quantifiable, he could find the answer to his question.
Planck wrote a mathematical equation involving a figure to represent individual units of energy. He called the units quanta . Planck assumed there was a theory yet to emerge from the discovery of quanta, but in fact, their very existence defined a completely new and fundamental law of nature. Einstein's theory of relativity and quantum theory , together, explain the nature and behavior of all matter and energy on earth and form the basis for modern physics. However, conflicts remain between the two. For much of his life, Einstein sought what he called a unified field theory -- one would reconcile the theories' incompatibilities. Subsequently, Superstring Theory and M-theory have been proposed as candidates to fill that role.
Quantum is sometimes used loosely, in an adjectival form, to mean on such an infinitessimal level as to be infinite, as, for example, you might say "Waiting for pages to load is quantumly boring."
a. The smallest amount of a physical quantity that can exist independently, especially a discrete quantity of electromagnetic radiation.
b. This amount of energy regarded as a unit.
2. A quantity or amount.
3. A specified portion.
4. Something that can be counted or measured.
5. A unit of acetylcholine, released at the synaptic cleft of a neuromuscular junction.