What does the weather forecast mean by ultraviolet rays?

UV is the abbreviation of ultraviolet ray. It is an electromagnetic radiation whose wavelength is shorter than visible light but longer than X-ray, and its wavelength range is 10nm-400nm. Ultraviolet light can be divided into three main areas: UVA (near ultraviolet light), UVB (middle ultraviolet light) and UVC (far ultraviolet light). UVA has the longest wavelength and the lowest energy, and can penetrate clouds and glass, causing certain damage to the depths of human skin. UVB has higher energy, which can cause sunburn, skin cancer and other problems in the sun. Most of the UVC that reaches the earth's surface is absorbed by the ozone layer and will not have a direct impact on the human body.