In some files is used referer (with one R) - en/acp/board.php:

'REFERER_VALID' => 'Validate Referer',

'REFERER_VALID_EXPLAIN' => 'If enabled, the referer of POST requests will be checked against the host/script path settings. This may cause issues with boards using several domains and or external logins.',

and in file en/acp/common.php:

'LOG_REFERER_INVALID' => '<strong>Referer validation failed</strong><br />»Referer was “<em>%1$s</em>”. The request was rejected and the session killed.',

In file en/acp/attachments.php is used referrer (with double R):

'SECURE_EMPTY_REFERRER' => 'Allow empty referrer',

'SECURE_EMPTY_REFERRER_EXPLAIN' => 'Secure downloads are based on referrers. Do you want to allow downloads for those omitting the referrer?',

I guess it should be unified.