Classically, the axis of a plant, consisting of stem and root;

Latterly, especially in Euphorbiaceae, used as an enlarged storage organ at soil level, composed of the swollen stem or root, or both.

The persistent, often woody base of an herbaceous perennial; also refers to the axis of a plant (including both stem and root).

The thickened base of the stem of certain plants such as some ferns and Dioscorea elephantipes.

Literally just the trunk of a tree in Latin, but used in botany to denote a stem that is long-lived, thick and not quite woody enough to be termed a trunk, for example, as in cycads. Succulent enthusiasts use it for the swollen stems of some desert shrubs, which they rather pretentiously refer to as ‘caudiciforms’, for example, Cyphostemma juttae.