Vandalism is one of the more serious offenses, and can be one of the quickest ways to a ban.
Some basic things defined as vandalism:
- Removing large amounts of stuff without a given reason.
- Changing or removing the bias of an article.
- Doing unwarranted edits to userpages with a Template:DontEdit on it.
- NOTE: Admins can edit userpages with DontEdits on them if said userpage contains rule-breaking content (such as spam categories).
- Undoing a constructive edit without a good reason.
Undoing edits without a good reason can quickly lead to a fight (known as an "edit war"), so it is a good idea to discuss beforehand.
Admins and other staff always get the final say as to what happens, and this can only be overturned by a court decision.
Repeated edit warring can get you banned.