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 and first appears in the episode "Reef Blower."
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.
The main mascot of the popular cereal brand Kelpo, Kelpy, is a piece of Kelp himself.