Need help with an error in my linked list class

Edit: I fixed my initial problem, but now I am getting this linker error that I can't figure out:

Hi guys, I'm trying to make a template linked list class, but I keep getting this error when I try to run the linked list class:

Code:

error LNK2005: "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl 
operator<<(class std::basic_ostream<char,struct std::char_traits<char> > &,class Term const 
&)" (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@ABVTerm@@@Z) already defined in poly.obj
1>C: ....... : fatal error LNK1169: one or more multiply defined symbols found

Code:

#include <iostream>
using namespace std;
#ifndef LISTP_H
#define LISTP_H

template<typename T>
class List
{
	friend ostream &operator<< <T>(ostream &, const List<T> &);
.
.
.
};

// Further down in the file
template< typename T>
ostream &operator<<(ostream &out, const List<T> &aList)
{
	T temp;
	for (i = 1; i <= size; i++)
	{
		aList.retrieve(i, temp);
		out << temp;
	}
	return out;
}

//In another class file
#include "llist.h"

class Term
{
	friend ostream &operator<<(ostream &, const Term&);
.
.
.
};

ostream &operator<<(ostream & out, const Term& data)
{
	if (data.exponent == 0)
		out << data.coefficient << endl;
	else
		out << data.coefficient << "x" << data.exponent << " + ";
	return out;
}

//Finally, main
#include <iostream>
#include "poly.h"
using namespace std;

int main()
{
	List<Term> ll;

	Term x(5, 11), y(12, 5), z(8, 0);
	if (x == 11)
		cout << x << y << z << endl;

	ll.insert(1, x);



	return 0;
}

It seems that the error is occurring because I defined two different operator << functions, but I tried commenting one out and that didn't help, so I can't figure out how to fix this one. Can anyone help me out?

You should never have "real" code in a header file. Templated code is okay (and in fact pretty much has to be in a header), but regular code, such as

Code:

ostream &operator<<(ostream & out, const Term& data)
{
	if (data.exponent == 0)
		out << data.coefficient << endl;
	else
		out << data.coefficient << "x" << data.exponent << " + ";
	return out;
}

must not appear in a header file.