Agar is a gelling agent that has been used in Japan since the 15th century. Agar agar is a plant-based gelling agent used in cooking and baking as a vegetarian alternative to gelatin. It is derived from seaweed and is available in a powder form. Agar agar is used to thicken, gel and set liquids and can be used in a variety of dishes including desserts, jams, and jellies.