No, electromagnetic waves are not a substance. Electromagnetic waves are a form of energy that can propagate through space or a medium without requiring a physical substance to carry them. They are created by the oscillation and interaction of electric and magnetic fields. Examples of electromagnetic waves include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. While these waves can interact with and affect matter, they are not themselves physical substances.