A rushlight is a tallow candle with a rush in the middle of it instead of a cotton wick. The rushes are coated with tallow by several successive dippings. The simplest kind of holder is made by splitting a stick and placing the rush diagonally in the opening.
The rushlight cannot stand upright, because it would burn too quickly. It has to be at an angle. Unlike candles, the rushlight cannot be left for more than a few minutes without attention.