Kelp are large () belonging to the (class Phaeophyceae) and are classified as the order Laminariales. There are about 300 different . Some species can be very long and form .
Kelp fisheries is a branch of fisheries science which deals with the study of and uses of large seaweeds of the brown algae group that are commonly called kelp.
Despite their plant-like appearance, scientists group them not with the terrestrial plants ( ), but instead place them either in or in .
Kelp grows in underwater "" () in shallow oceans. It requires nutrient-rich water below about 20 °C (68 °F). It is known for its high growth rate the genera and grow as fast as half a metre a day, ultimately reaching 30 to 80 m.
Through the 19th century, the word "kelp" was closely associated with seaweeds that could be burned to obtain (primarily sodium carbonate). The seaweeds used included species from both the orders Laminariales and . The word "kelp" was also used directly to refer to these processed ashes.