Wow, that's both an easy question as well as difficult to answer. In layman's terms, electromagnetic radiation could be categorized as any magnetic field created by electrical or electronic means....
A square.
Alpha, Beta, Neutron, X-ray, Gamma, Neutron radiation, Electromagnetic radiation, Visible light, Infrared, Microwave, Radio waves, Very low frequency (VLF), Extremely low frequency (ELF), Thermal...
All forms of nuclear radiation, including alpha, gamma, beta, neutron, are forms of energy.
One