A corm, bulbo-tuber, or bulbotuber is a short, vertical, swollen underground plant stem that serves as a storage organ that some plants use to survive winter or other adverse conditions such as summer drought and heat (perennation).

The word cormous usually means plants that grow from corms, parallel to the terms tuberous and bulbous to describe plants growing from tubers and bulbs.

A corm consists of one or more internodes with at least one growing point, generally with protective leaves modified into skins or tunics. The tunic of a corm forms from dead petiole sheaths—remnants of leaves produced in previous years. They act as a covering, protecting the corm from insects, digging animals, flooding, and water loss. The tunics of some species are thin, dry, and papery, at least in young plants, however, in some families, such as Iridaceae, the tunic of a mature corm can be formidable protection. For example, some of the larger species of Watsonia accumulate thick, rot-resistant tunics over a period of years, producing a structure of tough, reticulated fibre. Other species, such as many in the genus Lapeirousia, have tunics of hard, woody layers.

Internally, a typical corm mostly consists of parenchyma cells, rich in starch, above a circular basal node from which roots grow.

Long-lived cormous plants vary in their long-term development. Some regularly replace their older corms with a stack of younger corms, increased more or less seasonally. By splitting such a stack before the older corm generations wither too badly, the horticulturist can exploit the individual corms for propagation. Other species seldom do anything of that kind; their corms simply grow larger in most seasons. Yet others split when multiple buds or stolons on a large corm sprout independently, forming a tussock.

Corms can be dug up and used to propagate or redistribute the plant (see, for example, taro). Plants with corms generally can be propagated by cutting the corms into sections and replanting. Suitably treated, each section with at least one bud usually can generate a new corm.