Derived from the verb “to classify.” The process of placing an entity (item) of a universe into its category (pigeonhole) within a classification (scheme). This is a specialized function which requires a “judgment call” as to which category a given entity falls into in cases where the entity is described in a term or terms which are not found in the classification as printed (or its index). Classification requires expert knowledge of the universe of objects to be classified, in contrast to “coding,” which is a clerical task.