what is std cout in c++ code example

Example 1: std cout c++

#include <iostream>
using std::cout;
int main()
{ 
  	cout<<"Hello world";
    return 0;
}

Example 2: std::cout and cout

//c++
cout and std::cout both are same, but the only difference is that if we 
use cout, namespace std must be used in the program or if you are not 
using std namespace then you should use std::cout.