duck typing

    A term coined by Dave Thomas for a kind of
   dynamic typing typical of some programming languages, such
   as Smalltalk, Ruby or Visual FoxPro, where a
   variable's run-time value determines the operations that
   can be performed on it.

   The term comes from the "duck test": if it walks like a duck
   and quacks like a duck, it must be a duck.

   Duck typing considers the methods to which a value responds
   and the attributes it posesses rather than its relationship
   to a type hierarchy.  This encourages greater polymorphism
   because types are enforced as late as possible.

   
(http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/100511).

   (2006-09-13)