Maybe a not completely serious question but nonetheless I still feel this deserves clarification once and for all 
(also, maybe more people are similarly confused).
I always envisioned neural networks as a stack of layers, not unlike a pyramid. Logically, input would be on the bottom and output on top. But reading fastai code we seem to be referring to the top_model as being the part of the model that takes in inputs. I think I also came across similar naming convention in one of the papers.
Could I please ask if this is generally the naming convention to call the end of the model that takes in inputs the top and the predictions come out the bottom?