Answer:
The letter "X" is used to indicate X-rays.
Step-by-step explanation:
X-rays are a form of electromagnetic radiation, similar to visible light, but with much higher energy and shorter wavelength. They are used in various medical and industrial applications, such as radiography and computed tomography (CT) scans, as well as in scientific research. Because of its name , X-rays are often indicated by the letter "X" in medical imaging or other applications.