The term "concept" is trace back to 1550β60 (l. conceptum - something conceived), but what is today termed "the classical theory of concepts" is the theory of Aristotle on the definition of terms. As the term is used in mainstream cognitive science and philosophy of mind, a concept or conception is an abstract idea or a mental symbol, typically associated with a corresponding representation in a language or symbology. Concept has also been defined as a unit of knowledge built from characteristics.