Ultraviolet (UV) refers to a type of electromagnetic radiation that lies between visible light and X-rays in the spectrum. It is invisible to the human eye and is divided into three types: UVA, UVB, and UVC, each with different properties and effects. UV radiation is emitted by the sun and can also be produced artificially by sources like tanning beds and black lights. While UV radiation is essential for the production of vitamin D in the skin, excessive exposure can lead to harmful effects such as skin cancer and eye damage. Protective measures, such as wearing sunscreen and sunglasses, are important to mitigate these risks.