1. A mucilaginous substance, alginic acid, obtained from certain algae.
2. Any of several derivatives; such as, sodium alginate or alginic acid, of a gelatinous substance extracted from certain brown algae and widely used as a thickening, stabilizing, emulsifying, or suspending agent in industrial, pharmaceutical, and food products; such as, ice cream.
3. A viscous liquid, especially alginic acid or an alginate.

Source: seaweed. Use: thickener or emulsifier in plastics or food.