Excitation refers to the process in which an atom or molecule absorbs energy, causing its electrons to move to a higher energy level. This can occur through various means, such as heat, light, or electrical energy. When the electrons are excited, they may eventually return to their original state, releasing energy in the form of light or heat. In the context of physics, excitation is crucial for understanding phenomena like fluorescence and phosphorescence, where materials emit light after being energized. It also plays a significant role in quantum mechanics, as it helps explain the behavior of particles at the atomic level.