Also known as ‘agar-agar’ (the Malay term for jelly), agar is a substance derived from seaweed, and a useful vegetarian alternative to gelatin. It can be used to thicken soups, to make jellies (it’s especially popular in Japanese desserts), and as a clarifying agent for brewing.
It’s most commonly available as flakes or a powder, which forms a firm, clear, mostly flavourless jelly when mixed with water. You can buy it in Waitrose, in the home baking section, or online from Wing Yip.