A short, enlarged shoot system (PO:0009006) that has as parts a short stem (PO:0009047) in which the shoot internodes (PO:0005005) do not elongate, and one or more buds (PO:0000055) enclosed by fleshy leaves (PO:0009025) or leaf bases (PO:0020040).
May serve as a storage and/or perennating organ. Usually underground. A bulb differs from a corm (PO:0025355) by having fleshy leaves or leaf bases. The outer leaves of a bulb are often dry and membranous, rather than fleshy. May bear adventitious roots. Examples include Alium and Tulipa. Not the same structure as a bulbil.