X-rays are a type of light ray, much like the visible light we see every day. The difference between visible light and X-rays is the wavelength of the rays. Human eyes cannot see light with longer wavelengths, such as radio waves, or light with shorter wavelengths, such as X-rays.
X-rays can pass through nonmetallic objects, including human tissues and organs. An X-ray machine is like a giant camera that allows doctors to see what is going on inside a patient without having to do surgery.
To produce an X-ray picture, an X-ray machine produces a very concentrated beam of electrons known as X-ray photons. This beam travels through the air, comes into contact with our body tissues, and produces an image on a metal film.
Soft tissue, such as skin and organs, cannot absorb the high-energy rays, and the beam passes through them. Dense materials inside our bodies, like bones, absorb the radiation.