Wavelength. On the electromagnetic spectrum.
X-ray = 10^-10 meters.
Gamma ray = 10^-12 meters.
The shorter wavelength, the gamma ray, is more energetic.
What is the difference between x-ray and gamma ray?
Gamma rays and X-rays are very similar; however, gamma rays have a slightly high frequency than x-rays. They both have short wavelengths, but gamma rays have an even shorter wavelength than x-ray.
Because they are so similar, the focus of their differences is usually placed on the origin of the rays, as I'll explain below:
X-rays are produced from electrons which are located around the nucleus in an atom, whereas gamma rays are produced from a nucleus, located at the core of the atom itself.
Both x-rays and gamma rays are used in medical science, although to different effects. The video below explains in more detail the difference between x-rays and gamma rays, as well as how they are used on the human body.
Although, both these rays can be dangerous - in small doses they can have their benefits as the video shows.