Final answer:
An ostream in C++ facilitates output operations through classes while 'using namespace std' simplifies access to elements in the C++ Standard Library.
Explanation:
An ostream, short for "output stream," is a class in C++ that supports output and is available via <iostream> and in namespace std.
In C++, the statement cout << "Hello World!\n"; performs an output operation, printing a string to the standard output.
The usage of using namespace std allows omitting the prefix std:: when utilizing elements from the C++ Standard Library.
Learn more about C++ Streams and Namespaces here:
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