I want to add to this, that it would be good to multi-edit tags. I have dozens of tag imported from my Goodreads that I'd like to get rid of. And deleting them all individually from the tag list is huge timesink.

just a clarification to this since I had some confusion once, you have to click on the tag under a book to get to the "tag page" where you can delete. Clicking from the stats page will take you to a filtered list.

When you navigate to a tag page and click the "edit tag" button, there's an option to delete the tag at the bottom of the page. :)