I've used several IDEs and created several default projects. Upon creation, I'll find folder structures created for me. Sometimes I'll see a Resources folder, sometimes an Assets folder, and sometimes both. Is there actually a (standard) difference?
Most of the time I would consider them synonyms. They both serve as valid places to store non-source code items.
When both appear in the same project, the only difference I can come up with
I will say though that the difference is minor and outside of a few circumstances they should be considered synonyms.
It's a just a difference in terminology. In this context assets are the non-source code resources you use in your solution.