Classification

Classification is usually understood to mean the allocation of objects to certain pre-existing classes or categories. This distinguishes it from the earlier step in which the classes themselves are established, often through clustering in which similar objects are grouped together.^[1] Examples include a pregnancy test, identifying spam emails and deciding whether to give someone a driving licence.

Classification is a part of many different kinds of activities and studied from many different points of view including medicine, philosophy, law, anthropology, biology, taxonomy, cognition, communications, knowledge organization, psychology, statistics, machine learning, librarianship and mathematics.

As well as 'category', synonyms or near-synonyms for 'class' include 'type', 'species', 'order', 'concept', 'taxon', 'group' and 'division'.

The meaning of the word 'classification' (and its synonyms) may 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'; this overall activity is listed under Taxonomy. It may refer exclusively to the underlying scheme of classes (which otherwise may be called a taxonomy). Or it may refer to the label given to an object by the classifier.