A post that is completely identical to its parent, and was either uploaded afterwards or has no source while their parent does, and thus is inferior for Danbooru purposes.
Pixiv and Twitter posts are often identical, even if they have different filesizes. In 2019 Twitter stopped compressing as harshly as they used to, and in late 2020 Pixiv started losslessly recompressing their JPGs to strip metadata, so typically if there's only a few KBs of difference between two identical pictures from these two sites, it means they're the same exact image.
