self

class C  
    def C.x # self.x, C == self, self is C
        puts "Class method: <C.x> of class C"
        puts "self: #{self}"
    end
end

C.x # self.x

class C  
    def C.x
        puts "Class method: <C.x> of class C"
        puts "self: #{self}"
    end
end

class D < C  

end

C.x # self.x -> self is C
D.x # self.x => self is D

class Test
  def talk

  end
end 

obj = Test.new 
obj.talk
# same as self.talk