module

 module is like class,  but it can not be instantiated

 support methods for other class

 

use include to include module

a class can only have inherit from one class, but it can mix in more than one mouels

ex:

module Animal

    def   test

    ned

end 

class Rabbit

      include Animal

      def  run

           test

     end

end

if a class include two modules,  M1 & M2( M2 is included last),

M1 & M2 both have method test

When the object of the class calls method test,

it will call M2's test