Electromagnetic waves are waves that can travel through a vacuum (empty space). They don't require a medium or matter. They travel through electrical and magnetic fields that are generated by charged particles. Examples of electromagnetic waves include light, microwaves, radio waves, and X-rays.
Visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometers (nm), or 4.00 × 10−7 to 7.00 × 10−7 m. These wavelengths are between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).