What is a photon best defined as?

A photon is best defined as a quantum of electromagnetic radiation or light. This definition encompasses the fundamental nature of photons as both particles and waves, as they exhibit properties of both, a concept known as wave-particle duality. Photons are the smallest discrete amounts (quanta) of electromagnetic energy, which includes visible light, radio waves, X-rays, and other forms of electromagnetic radiation.

Photons carry energy and momentum but have no rest mass, differentiating them from other particles such as electrons or protons. They are essential in many physical phenomena, including the photoelectric effect, where light energy can cause the emission of electrons from a material.

Understanding photons is crucial in fields such as quantum mechanics and optics, where they play a significant role in how we understand light's interaction with matter. This definition incorporates the scientific principles underlying how light behaves and interacts with various materials, making it essential knowledge in physical science.