A hierarchy (from the Greek ἱεραρχία hierarchia, "rule of a high priest", from ἱεράρχης hierarkhes, "leader of sacred rites") is an arrangement of items (objects, names, values, categories, etc.) in which the items are represented as being "above," "below," or "at the same level as" one another.A hierarchy (sometimes abbreviated HR) can link entities either directly or indirectly, and either vertically or diagonally.