A Negotiable Instrument is an unconditional promise to pay a certain amount of money and no other undertakings.  It is like a courier without luggage.

Some notes are negotiable instruments, but not all.

When you buy a car, that note is not a negotiable instrument because that note has so many things with it.  You cannot just say pay to the order of…and endorse it over to someone else.  It is a note, but not a negotiable instrument.

Whereas, if you write a check to me, and I lose the check, someone who picks up the check can cash it.  A check is a negotiable instrument.

Similarly, most mortgages have notes that are negotiable instruments.  If you have the note, you can transfer enforcement of a forecloseA reverse mortgage note; however, is not a negotiable instrument—you cannot endorse it and hand it to someone—possession is not going to work.