22.1.2—A photon is a quantum of electromagnetic energy

A photon is a discrete packet of electromagnetic energy with energy proportional to frequency and zero rest mass.

Photons travel at c in vacuum and are absorbed or emitted as whole quanta in interactions.

A higher-frequency ultraviolet photon carries more energy than a visible red photon.

A photon is not a tiny classical wave crest, and increasing intensity increases photon number at fixed frequency rather than each photon’s energy.