InterWikis are a class of macros found on some Wiki site. They provide convenient context based-links to other sites, as shorts to typing the full URL.

Some examples:

• Google:Wikis becomes a hyperlink to http://www.google.com/search?q=Wikis
• MSKB:137247 becomes a hyperlink to KB Article 137247 http://support.microsoft.com/default.aspx?scid=kb;EN-US;137247

On FlexWiki, you can do these using the external Wiki capabiltiies (see ExternalReferencesFormattingRules) or, for more flexibility, through InterWikiBehavior.