Energy levels refer to the quantized values of energy that a quantum mechanical system can possess. In physics, energy levels are often used to describe the energy states of particles such as electrons in atoms or molecules. These energy levels are often depicted as discrete values, where each level corresponds to a specific amount of energy that the system can have. In atoms, energy levels are associated with the different orbitals that electrons can occupy, with higher energy levels corresponding to electrons being farther from the nucleus. Energy levels play a key role in understanding the behavior of quantum systems and are important in a wide range of fields, including chemistry, physics, and material science.