I have been searching for this, using "delete series" but couldn't find exactly what I was after, if this is a duplicate, I apologise.

In my "All Books" display, I have only 17 series showing. All are series actively being used in the metadata of the various books. However, when I add books to Calibre, the dropdown list in the "Series" box of the metadata window includes dozens of "ghost" entries - duplicates, typos, variant series names, etc., that have accumulated over the years. How do I find and delete these to make scrolling through the dropdown list less time-consuming when editing metadata