For those interested in exploring both fastai v1 and v2 source code, and wonder what a given variable name means you might check out the fastai Abbreviation Guide.
The guide is part of the fastai v1 documentation (v2 doesn’t have one yet AFAIK) but based on my own experience a similar convention is used for v2. We could add here the new variables names introduced in v2 to later update the original list.