The University of Maine's Sea Grant "Seafood Guide" lists seaweed. So it seems like seaweed can be considered seafood, but it does not seem to be common practice. .... Now, if this is purely a "practical" definition we're seeking here that will get you past customs, go with "vegetable" or "plant material". read more
In culinary it is a vegetable. Because it is a plant thrive on photosynthesis, can be eaten cooked or raw, and often served as a savoury food. It is not a fruit because it does not taste sweet and don’t contain seeds. read more
Seafood is a term used to describe edible marine fish and shellfish. Seaweed, while it does come from the sea, and is edible, is not considered seafood, any more than hooves or horns would be considered beef. It's not even really a weed. It's a marine alga or kelp. read more