Although we can't see them, gamma rays are simply another form of light. Gamma rays, light rays, x-rays and radio waves are all part of the electromagnetic spectrum.
Electromagnetic waves oscillate.
How fast they oscillate is called their frequency. The wavelength of an electromagnetic wave is the distance between wave crests. For an AM radio wave that distance is about 300 meters. The energy carried by an electromagnetic wave is proportional to its frequency. A typical gamma ray carries 3,000,000,000,000 times more energy than an AM radio wave.