On
Usenet, the process of
posting a new message that
replaces a previous one. Most
clients won't let you do this unless they
believe that you are the person that wrote the original, in order to reduce
abuse. However, it is fairly
trivial to forge a supersede header.
Fascinatingly, by far the most common error in creating a forged supersede is to spell it supercede.
Superseding a message is effectively equivalent to posting a cancel followed by a new message, but is accomplished in a single message. Like cancels, many servers do not honour supersedes due to large-scale abuse.