Electromagnetic waves are transverse waves. They transfer energy from a source to an absorber. For example, light from the Sun carries energy across space and warms the surface that absorbs it, and the microwaves in an oven carry energy from the oven to the food.
The waves form a continuous spectrum, with no gaps between the types. They are grouped by wavelength and frequency. Going from long wavelength to short wavelength, or from low frequency to high frequency, the groups are: radio waves, microwaves, infrared, visible light (red to violet), ultraviolet, X-rays and gamma rays.
All types of electromagnetic wave travel at the same velocity through a vacuum (space) or air. Our eyes only detect visible light, so we only detect a limited range of electromagnetic waves.
