Manual:$wgFallbackSkin

From mediawiki.org
Skins: $wgFallbackSkin
Fallback skin used when the skin defined by $wgDefaultSkin can't be found.
Introduced in version:1.24.0 (Gerrit change 148424; git #Ibd7485d)
Removed in version:still in use
Allowed values:(string)
Default value:'fallback'