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photon
/ˈfəʊtɒn/
This term describes the smallest possible discrete packet of energy that can exist in the electromagnetic spectrum. It carries no electrical charge and possesses zero invariant mass, moving always at the speed of light in a vacuum. In practical scientific discourse, the word is used to shift the perspective of light from a continuous wave to a stream of individual particles. This conceptual shift is essential for explaining phenomena like the photoelectric effect, where light interacts with matter as discrete collisions rather than smooth flows.
Used to count individual packets of light energy, such as when measuring a specific number of particles hitting a sensor.