These fields appear under the Send to / Don't send to boxes only when a selected group needs extra input:

• Trigger Date – used by groups ending in "on X day (Select day on next field)", such as Delivery on X Day, Pickup on X Day, or the "on X day" option for whichever other ordering modules (e.g. Catering) your account has enabled. Pick the delivery/pickup/order date; the audience is everyone with an order for that ordering method on that date.
• Trigger Compare Value – used by People with Digital Balance <=> X. Choose an operator (Lower (<), Lower or Equal (<=), Equal (=), Greater (>), Greater or Equal (>=)) and enter an amount, e.g. Greater (>) 20 targets customers with more than 20 in store credit.
• Trigger Checkouts Count – used by People who made more than X checkouts; enter the number of orders.

If you remove the group that needed the field, the field is hidden (and cleared before saving). The values are saved with the campaign and restored when you edit it.