Something most people avoid, even if they know better. The practice of periodically creating a mirror of important data and storing it separate from the main storage, allowing a system to recover from the loss of one or more storage locations.
The contents of this wiki is backed up periodically. All page changes are logged and saved. So while it's trivial to mess up this public wiki, it's also trivial to restore it. In most cases, the regulars here tend to remove all traces of people deliberately messing up the wiki. In some cases, we leave it and even discuss it (as in [L1 ]).
All in all, reason and good taste appear to prevail. So these backups are there mostly as insurance. Wiki's are a medium for optimists :) -jcw