A photon is a fundamental particle that represents a quantum of light or electromagnetic radiation. It is massless and travels at the speed of light in a vacuum, making it essential for the transmission of energy across vast distances in the universe. Photons exhibit both wave-like and particle-like properties, a concept known as wave-particle duality, which is a cornerstone of quantum mechanics. Photons play a crucial role in various phenomena, including the photoelectric effect, where light can eject electrons from materials. They are also integral to technologies such as lasers and fiber optics, enabling advancements in communication and medical imaging.