Source : Free On-Line Dictionary of Computing

operational semantics
     
         A set of rules specifying how the state of an actual
        or hypothetical computer changes while executing a program.
        The overall state is typically divided into a number of
        components, e.g. {stack}, {heap}, {register}s etc.  Each rule
        specifies certain preconditions on the contents of some
        components and their new contents after the application of the
        rule.
     
        It is similar in spirit to the notion of a {Turing machine},
        in which actions are precisely described in a mathematical
        way.
     
        Compuare {axiomatic semantics}, {denotational semantics}.
     
        (1996-08-21)