Because "X-ray" is the name that Konrad Roentgen gave to the waves he discovered,
which turned out to be shorter than ultraviolet but longer than gamma rays, and the
name stuck. If those same waves were longer, they would not be called 'X-rays'.
Generally the term "short wavelength" is used to describe light but it can be used for any wave. It means the distance between one wave front and another is only short. Given that, you might get the idea that "short wavelength" is a relative term. In radio, the term short wavelength is almost obsolete. If has been replaced by terms such as HF (High frequency) VHF (very high frequency) UHF (ultra high frequency) and so forth. The higher the frequency the shorter the wavelength. After radio waves, electromagnetic waves go to infrared, visible light, xrays then gamma rays as the wavelength gets shorter.
Short wavelength
Both a wave with long wavelength and a wave with short wavelength can have a lot of energy, or little energy.Specifically in the case of electromagnetic waves, a short wavelength corresponds to high energy - but this is only the energy PER PHOTON. But note that each of such waves usually consists of a lot of photons.
There is a simple answer and a complicated answer. The simple anser is, "Neither", the complicated answer is , "It depends."
short wavelength
No, X-rays have shorter wavelength than ultraviolet light. X-rays have wavelengths in the range of 0.01 to 10 nanometers, while ultraviolet light has wavelengths in the range of 10 to 400 nanometers.
Shortest wavelength is gamma rays. Next longer wavelength is with Xrays. Then Ultraviolet, visible radiations, infra red, microwaves, radio waves with shorter wavelength and radio waves with longer wavelength
The color of visible light with the longest wavelength is red; the color with the shortest is violet. So "ROY G. BIV" lists the colors from long to short wavelength. Just to confuse you, we'll also mention that it lists them from lowest to highest frequency.
Short wavelengths.
Radio waves ... including microwaves ... and X-rays are different only in wavelength (frequency). The sun radiates all of them.
Scattering of light
A short wavelength means higher energy