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any change produced in the surrounding by a system.
A variable at the boundary of an organism or machine through which information exits. The products, results or the observable parts (see subsystem) of a system's behavior (see allopoiesis). The medium through which a system may exogenously control others. The record left behind by a system of its own behavior. An output could conceivably include all of a system's behaviors, but it becomes an informative concept only if some of its variables remain inaccessible to an observer or have no effect. E.g., a computer prints or displays only the final results of a lengthy computation thus invoking the distinction between output and internal (intermediate and inaccessible) variables. Human cognitive processes remain similarly hidden from view and are therefore distinct from the primary verbal, manual and gestural output of man. Here, output is the overt manifestation of human (including cognitive and hormonal) behavior. (Krippendorff)