An electron is defined as a subatomic particle with a negative charge and a negligible mass compared to protons and neutrons. It is found in an atom's electron cloud, orbiting around the nucleus. Electrons have a property called spin, which determines their magnetic moment and gives rise to their behavior in magnetic fields. They also have wave-particle duality, meaning they can exhibit both particle-like and wave-like properties depending on the experiment being conducted. Electrons play a crucial role in various physical and chemical processes, such as electricity, magnetism, and the formation of chemical bonds.