A photon is a fundamental particle of light and other forms of electromagnetic radiation. It exhibits properties of both a particle and a wave, which is known as wave-particle duality.
In certain experiments and observations, the behavior of photons can be explained by treating them as particles. Photons can be detected and interact with matter as discrete entities with specific energies and momenta. For example, in the photoelectric effect, photons behave as particles when they transfer their energy to electrons, causing them to be ejected from a material.
On the other hand, photons also exhibit wave-like properties. They can interfere with each other, diffract around obstacles, and exhibit phenomena such as polarization and interference. These wave-like characteristics are described by the mathematical formalism of waves, such as the wave equation of electromagnetic fields.
Wave-particle duality is a fundamental concept in quantum mechanics, and it applies not only to photons but also to other particles, such as electrons and other fundamental particles. It implies that particles can exhibit both particle-like and wave-like behavior, depending on the experimental setup and the observed phenomena.