Ever tried to empty the trash on your Mac, only to be told that "Operation can't be completed because the item [file name] is in use." Sometimes it is in use, and you must halt the process that’s using the file or let it finish before taking out the garbage.
However, I’ve found that there are times when an item WASN’T in use, but macOS thought it was. In this case:
Double-click on your Mac's Trash bin in the app dock.
Choose the item you want to delete.
Right-click on the item.
Select Delete Immediately from the dropdown menu.
Click Delete to confirm that you want to delete the item. Note: you can't undo this action.
Voila! Now you can empty the trash.
(This how-to is based on my experiences and info on Apple's support pages — where the images sometimes come from.)