Classification

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Classification is usually understood to mean the allocation of objects to certain pre-existing classes or categories. This distinguishes it from clustering in which similar objects are grouped together, thereby creating new classes.^[1]

Classification is a part of many different kinds of activities and studied from many different points of view including philosophy, law, anthropology, biology, taxonomy, cognition, communications, knowledge organization, psychology, statistics, machine learning, librarianship and mathematics. In the theory of measurement, classification is understood as measurement against a nominal scale.

As well as 'category', synonyms or near-synonyms for 'class' include 'type', 'species', 'order', 'concept', 'taxon' and 'division'. Equally, the meaning of the word 'classification' (and its synonyms) may in day-to-day usage take on one of several related meanings: it may encompass both classification and the creation of classes, as for example in 'the task of categorizing pages in Wikipedia'; or it may refer to the underlying scheme of classes; or it may refer to the label given to an object by the classifier.