Seaweed refers to a type of marine algae that grows in saltwater. It is commonly found in oceans, seas and other bodies of water around the world. Seaweed comes in various forms such as kelp, nori, wakame, and agar-agar among others. These plants are known for their ability to photosynthesize like land plants but they lack a true stem, root system or flowers. They have been used by humans for thousands of years for food, medicine, and other purposes such as making cloth and paper.