Commercial vs. (MF) Residential RE? Which Mortgage?

[Ramsey Rimkeit]

What's the difference between Commercial and Residential Real Estate when it comes to multifamily properties with 5 or more?

I keep reading definitions of Commerical Real Estate that don't implicitly exclude larger multifamily investments. 

I imagine anything bigger than 4 units would be considered commercial real estate? If you own a 4-plex but don't live in it, is it still residential? Or is anything that includes residential units automatically only residential real estate? What about hotels? Airbnb?  

I'm asking because I'm looking into refi opportunities for multifamily properties in approx. the 10-20 unit range. Will I still be looking at residential mortgages?

I have an appointment with a loan officer on Tuesday and I want to be as informed as possible before I ask any stupid questions. I have listened to the section on mortgages in both the BRRRR book and the Long-Distance REI books by David Greene for questions but he doesn't go into this finite difference.