I googling around about the difference between tracing, copying and referencing since YouTube have been shoving a lot of that (plus arts dramas that I didn't even know actually exist) to my face.
Then on the very first link is this :
I think it's pretty legit, and with that there's my understanding :
Tracing : you're tracing another person arts,pictures/models, by putting the arts below it and trading it line by line, maybe with some difference from the original.
Copying : you're copying another person arts, pictures/models (like Jenny explanation), but it is not the same as tracing, since you made the arts yourself but with no much difference from the original.
Referencing : you draw your own arts by using the original picture as reference, but not copying since you're not drawing it the same and only took parts of the reference and upgrade everything with your own style.
At least this my understanding of it and my explanation might be a bit wonky but you jet what I mean.
Feel free to point out what I say wrongly.