An X-ray is a form of electromagnetic radiation.  X-rays have extremely short wavelength and high frequency, with wavelengths ranging from about 10−8 to 10−12 metres (m) and corresponding frequencies from about 1016 to 1020 hertz (Hz).

X-rays are a type of ionising radiation with many uses.  Most people know their use in medicine to take images of the human body highlighting hard objects like bones.  They are also used to destroy cancerous cells allowing some forms of cancer to be treated.  Outside of medicine, these properties are used to sterilise materials and inspect the structural integrity of structural materials.