iostream vs ostream what is different?

Question

As the book says (Exploring C++: The Programmer\'s Introduction to C++):

The istream header declares input operators (>>), and ostream declares outp

Answer 1

So After that; I sent email to Bjarne Stroustrup and He replied just like that:
Personally, I always use iostream and you never need both. ostream exists so that people can #include only the minimaldeclaration needed.