UV flashlight is a special kind of flashlight. They don't emit high lumen values to illuminate the field of view like traditional flashlights. Instead, they make certain things, signs and materials visible through ultraviolet light.
As the name suggests, UV flashlights emit ultraviolet light. This allows the human eye to see things like markings or substances. This is because these things are invisible to humans under normal daylight or LED lights and cannot be perceived with any senses.