This constant sets the time after which SPIP deletes accounts in the spip_authors table which have been recently created but for which the user has never validated the creation request.
This delay is set in seconds. By default, it is set to 45 days.
Example:
define('_AUTEURS_DELAI_REJET_NOUVEAU', 7 * 24 * 3600);
will ensure that recently created but unauthenticated accounts are destroyed after a delay of only one week.