The weekly digest is an email that contains a weekly summary of orders, shipments, revenue, and shipping costs.
Anyone with Administration user permissions has the ability to opt in or out of the Weekly Digest email.
If you want to prevent a user on your account from getting the Weekly Digest, then you will need to edit the permissions on their user name. Ensure that the user does not have Reporting or Administration permission, and they won't get the Weekly Digest emails going forward.