What is MTN (Medium Term Notes)?

I get all day people asking if I have MTN (Medium Term notes? Then they ask me question which Bank it was issued? Or some time people come to me and say they have MTN whether I want to buy it? If I asked them then they it is under contract $50 Billion USD per day upto $500 Trillion USD and Deutsche Bank is the issuer but it is under contract so they cannot provide me any ISIN or any documentation. They say it is European paper. Can some one explain me what it is actually or it is just a broker joker stuff. I have no idea any notes or papers exist on this planet could be upto 500 Trillion USD.