Hierarchies
From The Glossary of Digital Photography
A method of organization used in computers to specify the order of operation in software application. Hierarchies are often used by digital photographers to set up folder-based organizational systems for their images. Folders are arranged inside other folders in hierarchies. Keywords are also set up in hierarchies, using parent and child keywords. For example, the parent keyword mammal could have child keywords of dog, cat, deer, and rat.
