In short: Group conditions (on product discounts) and Included Items conditions (on order discounts limited to collections) only look at the items that discount targets, not the whole cart.
Group conditions on product discounts
The "group" is the set of cart items this product discount targets, after exclusions. For a discount on the Summer Collection with sale items excluded, the group is the full-price Summer Collection items.
Group Subtotal: the value of the group, before discounts.
Group Total: the value of the group after this discount. If a product discount type listed above this one already discounts some of the same items, those savings are taken off too.
Group Quantity: the number of items in the group.
Item has subscription: set Value to Yes to discount only subscription items, or No to discount only one-time purchases.
Worked examples
Buy 2 from the collection, get 10% off them: Group Quantity, Greater than or equal to,
2.10% off the collection once those items reach $150: Group Subtotal, Greater than or equal to,
150.Group Total is for "after discount" thresholds. A 20% discount with Group Total at least $100 needs $125 of group items, because $125 − 20% = $100.
Included Items conditions on order discounts
When an order discount uses Limit to collections, you get two extra conditions. They only count items from the chosen collections:
Included Items Subtotal: the value of those items, before discounts.
Included Items Quantity: the number of those items.
Example: 15% off Gift Sets once the customer has at least $75 of Gift Sets. See Order discounts.
Good to know
Excluded items (sale or subscription) never count toward Group conditions. To count them, use Cart Quantity or Cart Subtotal instead. See Sale items and subscription items.
Item has subscription works as a filter, not a pass-or-fail rule. With Yes, subscription items get the discount and one-time items in the same cart don't.
Group conditions are only available on product discounts, and Included Items conditions only on order discounts with Limit to collections.