A loosely woven cord (in a candle or oil lamp) that draws fuel by capillary action up into the flame WordNet 3.0 & Open English WordNet

A string that holds the flame of a candle. OmegaWiki

A bundle, twist, braid, or woven strip of cord, fabric, fibre/fiber, or other porous material in a candle, oil lamp, kerosene heater, or the like, that draws up liquid fuel, such as melted tallow, wax, or the oil, delivering it to the base of the flame for conversion to gases and burning; any other length of material burned for illumination in small successive portions. Wiktionary

The porous cord that draws up liquid fuel for burning. Wiktionary (translation)