Edit
This tag is used to indicate that a post's revision at the source is bad, and should not be uploaded.
A revision can be bad for any of these reasons:
Note that this tag is supposed to be used on image that are already tagged with md5 mismatch, not on revisions that are actually already uploaded. Images that use this tag should also have some amount of visual identity or sameness to the revision at source, and this should not be tagged on images that have actual revisions even if they are smaller resolution (post #2561932, post #2749109) or deficient in other respects. In other words, the deficiency should be the only change between the image on Danbooru and the revision at the source.
See md5 mismatch for more information on uploading revisions.
See also
The following tags are aliased to this tag: bad_revision (learn more).