What is the tag 'Orphan'?

I didn’t create a tag ‘Orphan’! I suddenly saw a lot of untitled document when I checked all notes two weeks ago which were not created by me. They are all tagged with ‘Orphan’. Is this a bug? Is it safe to delete all the untitled document?

This is the screenshot when I was viewing the tag “Orphan”

The Orphan Power-up is not a bug, it’s a collector for (from what I can tell) rem that had a parent, but now no longer do, and are not tagged as Document. The load of empty rem is a bug, but I don’t know what causes it (possibly something to do with portals or creating rem via inline searches). You should be able to delete them, though in some cases they seem to resurrect themselves. Feel free to shoot a report using the “Report Bugs” button accessible from the ? button in the lower right of the app.