Celery cabbage (Brassica pekinensis), is a species of mustard cultivated for its edible leaves. For the prepared condiment see Mustard (condiment. For other uses of the term "mustard" see Mustard. In general terms eating (formally ingestion) is the process of consuming Food to provide for the Nutritional needs of an Animal, particularly In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis.