The Electromagnetic Spectrum is the spectrum of Electromagnetic waves. There are Radio waves, Microwaves, Infrared Waves, Visible Waves, Ultraviolet Waves, X-Rays, and Gamma Rays. Each have every day uses such as listening to the radio or treating cancer. Each kind of wave has a different frequency and wavelength. If a wave has a longer wavelength than it will have a shorter frequency.
Radio Waves are the largest Electromagnetic waves on the list. They can be as long as a building or they can be longer that the Earth's diameter! Radio waves have the longest wavelengths and the smallest frequency. Radio waves are used for listening to the radio and using Radar. Radio waves can also be used to transmit data to satellites and computer networks.
(Disclaimer: This is not a picture of an actual wave. It's a picture of a microwave oven)
Microwaves are the second longest wavelengths and second smallest frequencies. Microwaves have uses just as Radio waves do. Microwaves are used for cooking food as seen above. They are also used for transmitting data between cell phones and other devices like them.
Next on the list is infrared waves. Infrared waves have the third longest wavelengths and the third smallest frequencies. Infrared waves are emitted by the sun and they are what make us feel heat. Certain TV remotes even emit infrared waves to tell your TV what to do. Infrared waves cannot be detected by human eyes so we have special cameras that can interpret the waves. They then assign visible colors to them so that we can understand the data for ourselves.