Manual:$wgDefaultRobotPolicy

Robot policies: $wgDefaultRobotPolicy
Allows specifying the default robot policy for all pages on the wiki
Introduced in version:1.12.0 (r30602)
Removed in version:Still in use
Allowed values:(text string appropriate for a "robots" meta tag)
Default value:'index,follow'

Details

Allows specifying the default robot policy for all pages on the wiki. The default is to encourage indexing and following of links. This can be overridden on a per-namespace and/or per-article basis.

e.g.

$wgDefaultRobotPolicy = 'noindex,nofollow';
$wgNamespaceRobotPolicies = [
     NS_MAIN => 'index,follow'
];

would forbid indexing and following of links on all pages outside the main namespace.

See also