Interesting answers.
It seems like there really isn't one clear answer though.
IMO they are the same thing. Leave-ins moisturize, and you leave in moisturizers. Maybe that's just me though.
a hair dresser once told me a regular conditioner could not be used as a leave in on relaxed hair b/c it continues to soften it and break it down.
so, that is my take on it. Now that I am nautral, I do use regular conditoiner as a leave in with no trouble