Source : Free On-Line Dictionary of Computing

dynamic binding
     
        The property of {object-oriented programming} languages where
        the code executed to perform a given operation is determined
        at {run time} from the {class} of the operand(s) (the receiver
        of the message).  There may be several different classes of
        objects which can receive a given message.  An expression may
        denote an object which may have more than one possible class
        and that class can only be determined at run time.  New
        classes may be created that can receive a particular message,
        without changing (or recompiling) the code which sends the
        message.  An class may be created that can receive any set of
        existing messages.
     
        {C++} implements dynamic binding using "{virtual member
        function}s".
     
        One important reason for having dynamic binding is that it
        provides a mechanism for selecting between alternatives which
        is arguably more robust than explicit selection by
        conditionals or {pattern matching}.  When a new {subclass} is
        added, or an existing subclass changes, the necessary
        modifications are localised: you don't have incomplete
        conditionals and broken patterns scattered all over the
        program.
     
        See {overloading}.