All kelp is seaweed, but not all seaweed is kelp
Seaweed is a general term for marine macroalgae, and includes over 10,000 different species and counting. Macro algae are large algae that grows in the sea. Seaweeds use light from the sun, carbon dioxide and nutrients from seawater to grow. Seaweed can vary in shape, color, size, and flavor. Seaweed are in three groups — red, brown, and green. Kelp fall under brown seaweeds.
Check out Dr. Mandy Lindberg’s https://www.seaweedsofalaska.com for a complete guide to seaweeds of Alaska