One or more items can be deleted as part of a Custom Action. The "Run for" section determines which item (or set of items) is deleted.
Run for section:
Current item -- The item from which this Custom Action is initiated will be deleted.
Lookup -- If the current item has any Lookup columns, these will be listed (Note that if the Lookup column is set to "Allow Multiple Values", it will not show up in the list).
Choose one of the Lookup columns listed. When the Delete Item action is run, the item in the Lookup list will be deleted.
For example, there may be a Ticket list with "Category" as a Lookup. The Category list is a separate list that populates a drop-list on the Ticket. A Delete Item action can be run on the Ticket that will delete the Category associated with the Ticket. That is, it will delete the Category from the Category list even though the Delete Item action is run from the Ticket list.
Query List Action item(s) -- the items returned from a preceding Query List action will be deleted.
