The electromagnetic spectrum is the range of electromagnetic radiation frequencies in the universe, which includes radio waves, x-rays, all kinds of light, gamma rays, etc. The reason the Em spectrum is segregated as such is because of its common interaction with matter. For example: gamma rays tend to create particle, anti-particle pairs when interacting with other matter, infrared rays tend to vibrate molecules in matter. This radiation is known to occur any time charged particles are accelerated, and create both electric and magnetic fields perpendicular to each other, hence the name.
For a long time scientists believed there was no limit on this range, only a limit on what we could detect. So, is there a limit? Actually, yes.
Scientists now surmise that the upper limit on the wavelength of EM radiation is the width of the universe itself. The lower limit, however, is a constant called a Planck length. This is the theoretic smallest length of anything possible in the universe, and is1.61619997 E -35 m.
Most importantly, this radiation allows scientists to look where visible light could never go. X-rays are frequently used to scan patients for damage, and every scan the universe for new discoveries. We'd be pretty far behind in astronomy without this powerful stuff.