Classification is one of the basic types of supervised prediction, where the task is to identify to which of a set of categories (sub-populations) a new observation (or instance) belongs, on the basis of a training set of data containing observations (or instances) whose category membership is known. An example would be assigning a given email into "spam" or "non-spam" classes or assigning a diagnosis to a given patient as described by observed characteristics of the patient (gender, blood pressure, presence or absence of certain symptoms, etc.).

See statistical classification on Wikipedia.

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