A wick is a narrow tube or string that serves as a conduit for the flow of liquid, typically in a candle or lamp. It's usually made from cotton or other absorbent materials and its main function is to draw fuel upward from the reservoir to the flame by capillary action. The wick helps to distribute the heat evenly across the surface of the liquid, preventing it from boiling rapidly or burning out too quickly. In essence, a wick plays an essential role in maintaining the stability and longevity of a light source.