Purpose of "import std;" in C++

I have seen following small piece of code on cppdepend site.

import std; // Module import directive.
int main() 
{
    std::cout<<"Hello World\n";
}

So, What is the purpose of import std; in C++? How to use import std; instead of using namespace std; in C++?

I tried to compile program in G++ compiler, but I got an error.