Namespace is a new concept introduced by the ANSI C++ standards committee. This defines a scope for the identifiers that are used in a program. For using the identifiers defined in the namespace scope we must include the using directive, like using namespace std;
Here, std is the namespace where ANSI C++ standard class libraries are defined. All ANSI C++ programs must include directive. This will bring all the identifiers defined in std to the current global scope. using and namespace are the new keywords of C++.