What *exactly* goes in "Reports"?

I know not everyone will be invited to submit a report, but take this as open/general question.

What exactly is expected from the reports? e.g. can you provide clear instructions on what you expect, e.g. a single(1) PDF? any additional artifacts?

The description shows “how” the report will be evaluated, but it seems “what” must be provided its entirely open?

Thanks.