Definition
Answer form is the shape an assistant chooses for its reply: a ranked list of named options, an unranked list, or guidance that names nobody at all. It is a property of the question and the engine, not of any brand.
Why it matters
Questions that produce guidance without names are open ground: no competitor holds them either, and they are usually cheaper to win than displacing an incumbent from a ranked list.
How to measure it
Classify each answer by form and look at the no-names group first when planning content. Track how the share of ranked lists changes over time, since a category hardening into ranked lists is getting harder to enter.