Invoice Alignment is our term for limiting the contents of an invoice to a particular period.  Typically you would use this when a customer only wants shipments for one month at a time on their invoices.

For example, if your customer wants an invoice in July that only has June shipments in it, even though they have billable July shipments, you would use this feature.

This is a per-customer setting so you edit it in the Customer Properties.

Setting Invoice Alignment to None has no effect.  Setting it to Previous Week means that the shipment date must not be in the current week in order to appear on the invoice.  Shipments older than the previous week will appear so this cut-off only affects the most recent shipments.  Setting it to Previous Month has a similar effect but the cut-off date is pushed back to the end of the last calendar month.