The more concrete the better: what's done by hand today, how many people would use it, and what has to come out the other end. That's enough to estimate without needing a meeting.
In a sentence or two. If it lives in a spreadsheet or a notebook today, say so — that already tells us a lot.
How many people, on what devices, and whether they need to see different things depending on their role.
The report, the statement or the file someone else is going to review. That's almost always what defines the whole system.
If there's a date that doesn't move —a close, an assembly, a season— it's better to know it up front.