The Planck unit is a set of natural units that are based on fundamental physical constants. These units are designed to simplify the equations of physics by using universal constants such as the speed of light, the gravitational constant, and Planck's constant. The most commonly referenced Planck units include the Planck length, Planck time, and Planck mass. Planck units are significant because they represent scales at which classical physics breaks down and quantum effects become prominent. For example, the Planck length is approximately 1.6 \times 10^-35 meters, which is incredibly small and relevant in theories of quantum gravity.