Kelp is a type of algae seaweed that makes up the order Laminariales. There are about 30 different genera. It is a very commonly used ingredient in most foods and drinks sold in Bikini Bottom.
Kelps are large brown algae seaweeds that grow in "underwater forests" (kelp forests) in shallow oceans, and is thought to have appeared in the Miocene, 23 to 5 million years ago. The organisms require nutrient-rich water with temperatures between 6 and 14 °C (43 and 57 °F). They are known for their high growth rate—the genera Macrocystis and Nereocystis can grow as fast as half a metre a day, ultimately reaching 30 to 80 metres (100 to 260 ft).
In the SpongeBob SquarePants series, kelp is a prominent ingredient used in a wide variety of foods and drinks. Most products that contain it have their names as parodies of foods that are sold in the real world, with the word "kelp" in place of a word in the food's real name.
There is also a forest that revolves around the plant called Kelp Forest.