Just curious : Is there a difference between a book drop and a book return?

The only thing I would add is that the inside drop-off gets cleared frequently when the branch is open while the outside might be cleared as infrequently as once per day. I've had an item become damaged when I left it in the outside drop - never with the inside.

Not really. Either describes the receptacle for receiving books and other items that are.being returned. Some are inside the library, some are through outside walls for use when the library is closed, and some are free-standing boxes located outside near the library. All can be called by either term.