Quantum (noun)

1. A fixed or minimum amount of something, especially energy or a physical property.
2. The smallest possible unit of a physical property, such as energy or charge.
3. A discrete unit of a physical property, such as energy or charge, that can exist in a quantum state.

Origin:

From the latin word quantus meaning "how much" or "how great".

Examples:

1. The photon is a quantum of light.
2. The electron is a quantum of electricity.
3. The energy of an atom is quantized.
4. Quantum mechanics describes the behavior of matter and energy at the atomic and subatomic level.
5. The quantum computer is able to perform certain calculations much faster than a classical computer.