Η εφαρμογή, η εκτέλεση (ενός σχεδίου, μιας σκέψης, μιας ιδέας κ.τ.λ.)
A mapping from a pairing of mathematical objects to one of them, respecting their individual structures. The pairing is typically a Cartesian product or a tensor product. The object that is not part of the output is said to act on the other object. In any given context, action is used as an abbreviation for a more fully named notion, like group action or left group action.