### Hierarchy A tree structure. Also selectable as a custom field type. Custom fields of type hierarchy contain a hierarchical structure of items. ### Item An entity within a hierarchy. Can have other items as children. Items within the same parent item (siblings) maintain an order. ### Label A descriptive name of an item inside a hierarchy. This is a mandatory attribute. ### Root A specific item. It has no label and no short and is directly connected to the custom field of type hierarchy. The root has only a functional purpose, it cannot be edited by an admin nor selected by a user as a custom field value. ### Short A short (or short name) is an abbreviation for any item. It is optional, and items with and without shorts can easily live next to each other.