A bad page name violates naming conventions, triggers flaws in the software, uses avoidable plurals, is a spurious subpage, has Capitals In The Title Without Being A Proper Name and CapitalsInTheMiddleOfWords. It probably has a colon in it that will be mistaken for a wiki subspace by users of real wikitext.
See also list of bad page names and discussion of impact of bad page names and why tolerating them is a serious problem in general.
See also list of bad page names and discussion of impact of bad page names and why tolerating them is a serious problem in general.