Celery seed comes from celery, which is used around the world as a vegetable, either for the crisp petiole (leaf stalk) or the fleshy toproot.
In temperate countries, celery is also grown for its seeds. Actually very small fruit, these "seeds" yield a valuable volatile oil used in the perfume and pharmaceutical industries. They also contain an organic compound called apiol. Celery seeds can be used as flavoring or spice, either as whole seeds or ground and mixed with salt, as celery salt. Celery salt can also be made from an extract of the roots. Celery salt is used as a seasoning, in cocktails (notably to enhance the flavor of Bloody Mary cocktails), on the Chicago-style hot dog, and in Old Bay Seasoning.