The relevant conceptual distinction seems to be whether the aerodynamics of the blade(s) are conceptually independent, or interdependent. Better explained here

The relevant conceptual distinction seems to be whether the aerodynamics of the blade(s) are conceptually independent, or interdependent. Better explained here: https://en.wikipedia.org/wiki/Propeller_(aeronautics)#Aircraft_fans https://en.wikipedia.org/wiki/Propeller_(aeronautics)#Aircra...