A slug in WordPress is the exact final part of the URL that identifies a specific page, post, category, or tag. I recently edited the slug for my Single-Page AI Comics gallery and unwittingly broke the links in my blog posts that point to new content I uploaded at the time. The links are now fixed.
Moving my Michael Myers content to its own page also broke the links for those blog entries, and they’re fixed now, too.
In summary, if you’ve tried accessing my content via my blog posts and encountered an error, that was why.