Planck refers to Max Planck, a German physicist who is best known for his role in the development of quantum theory. In 1900, he introduced the concept of quantization of energy, proposing that energy is emitted or absorbed in discrete units called quanta. This groundbreaking idea laid the foundation for modern physics and changed our understanding of atomic and subatomic processes. The term "Planck" is also associated with the Planck constant, a fundamental constant in physics that relates the energy of a photon to its frequency. This constant is crucial in quantum mechanics and helps explain phenomena such as the photoelectric effect, which was later explored by Albert Einstein.