In a little more detail...

Sambal Oelek, also called sambal ulek or Sambal Oelek or just chili paste, is a bright red, thin and sharp tasting chili, often sold as a paste. Some types of this variant call for the addition of salt or lime into the red mixture. "Oelek" is a Dutch spelling which in modern Indonesian spelling has become simply "ulek"; both have the same pronunciation. Ulek is Indonesian special stoneware derived from prehistoric household kitchenware that is still being used actively in most Indonesian kitchens, particularly in Java. It is a stone pestle (called ulekan) with a mortar (ulek-ulek) made from an old and matured bamboo root, that is used for crushing chilies, peppers, shallots, peanuts, and other kinds of ingredients. Other sambal oelek products in the markets are: Sambal Oelek by Huy Fong, Sambal Oelek by Conimex, Sambal Oelek by Kokita