Weekly Order Email
The weekly order email is sent as part of the weekly cycle to tell customers if they have an order for the current week. The default email will include the customer's order contents, the cutoff time for any changes, and of course the body of the email that you write on the email templates page for the template 'Weekly Order Email'.
As part of the weekly cycle, one option you have is to send the email to ALL customers, not just people who are receiving an order.
If you select this option, the 'Weekly Order Email' will be generated for all active customers, even if they don't have an order.
Weekly No Order Email Template
As of May 2018- there is a new email template called 'Weekly No Order Email'. If you add content to this email and you have elected to send the weekly email to ALL customers, this is the email template that will be used for customers that do not have an order.
This new email template was introduced to help lessen confusion, and allow you to send a different, customized email to customers that are not scheduled to receive an order for the current week, hopefully encouraging them to log in and create an order on their off week.
To edit the email, just go to the Email Templates page on the admin and click the wrench next to the email template 'Weekly No Order Email':
After generating the weekly email in the system, you can check the pending email queue to see that both weekly order emails and weekly no order emails were created: