The interim scheme is optional functionality that can be used if an active scheme ends before a replacement scheme, or proposal, is activated. An interim scheme is a placeholder that allows the continued accrual of rebate earnings and optionally the allocation of cash. It is a locked scheme and can only be created by either manual or automatic replication of an active scheme to the next period. The activation of a proposal can be set to replace the corresponding interim scheme(s).
You can read more about Interim Schemes here.