Source : Free On-Line Dictionary of Computing

recursive type
     
        A data type which contains itself.  The commonest example is
        the list type, in {Haskell}:
     
        	data List a = Nil | Cons a (List a)
     
        which says a list of a's is either an empty list or a {cons
        cell} containing an 'a' (the "head" of the list) and another
        list (the "tail").
     
        Recursion is not allowed in {Miranda} or Haskell {synonym
        type}s, so the following {Haskell} types are illegal:
     
        	type Bad = (Int, Bad)
        	type Evil = Bool -> Evil
     
        whereas the seeminly equivalent {algebraic data type}s are
        acceptable:
     
        	data Good = Pair Int Good
        	data Fine = Fun (Bool->Fine)