The photon is the quantum of the electromagnetic four-potential, and therefore the massless bosonic particle associated with the electromagnetic force, commonly also called the "particle of light". Use this tag for questions about the quantum-mechanical understanding of light and/or electromagnetic interactions.
A photon, which belongs to the class of bosons, is the smallest discrete amount or quantum of electromagnetic radiation. It might be the most familiar of elementary particles. As photons are massless, they are travelling at the constant speed of light $(= 2.998 \times 10^8 \ \text{m/s})$ and bombard us daily from the sun, moon, and stars. For more than a century, scientists and engineers have harnessed them in aggregate to illuminate our cities and, now, our screens.
The energy of the photon depends on its frequency (how fast the electric field and magnetic field wiggle). The higher the frequency, the more energy the photon has. Of course, a beam of light has many photons. This means that really intense red light (lots of photons, with slightly lower energy) can carry more power to a given area than less intense blue light (fewer photons with higher energy).
As per Einstein’s light quantum theory, photons have energy equal to their oscillation frequency times Planck’s constant.
References:
What exactly is a photon? Definition, properties, facts
Light: The Physics of Photons
What, exactly, is a photon?
