Celery seed is a tiny, aromatic spice harvested from wild celery, known for its strong, earthy, and slightly bitter flavor. It’s often used to season pickles, dressings, soups, and spice blends, adding a concentrated celery taste without the bulk of fresh stalks.Celery seed is a tiny, aromatic spice harvested from wild celery, known for its strong, earthy, and slightly bitter flavor. It’s often used to season pickles, dressings, soups, and spice blends, adding a concentrated celery taste without the bulk of fresh stalks.