Why is this defined in this header ?

[Nezar]

Why is NODE_H defined in the code below ?

#ifndef NODE_H
#define NODE_H
#include <iostream>

using namespace std;

template<class T>
class Node
{
    public:
        Node();
        Node(const T& item, Node<T>* ptrnext=NULL);
        T data;
        Node<T>* NextNode();
        void InsertAfter(Node<T>* p);
        Node<T>* DeleteAfter();
        Node<T>* GetNode(const T& item, Node<T>* nextptr= NULL);
    private:

        Node<T>* next;
};

#endif 

[cronopio]

The name .h file...

[booradley60]

http://en.wikipedia.org/wiki/Include_guard

[Nezar]

Thanks.