A post whose source is a direct link to the image, rather than the page containing the image. For example, a Twitter image link instead of the Twitter post. The Twitter post is preferred because it's not possible to get to the Twitter post from the Twitter image.
If you see this warning on the upload page, it means you should upload the page containing the image, rather than the image itself.
Compare with bad id, where the source is deleted, and bad source, where the link does not point to the original image.
Image links that can be converted to the page containing the image, such as Pixiv image links, don't count for this tag.
