Any small vessel that could be filled with oil, fitted with a cotton or straw wick and then lit. The most common examples are long stemmed Shiwan pottery pieces with a small shallow bowls placed on top for the oil and wick. The item itself very much resembles a candle stick holder. Oil lamps are still used in temples in Tibet (yak butter or ghee), China and Hong Kong, often common cooking oil are used. The Tibetan ones have a ritual function, in that the butter is burned as an offering.