Nothing formal. It helps to know the problem you want solved, who will use the product, your budget range and timeline, and any designs, documents or links to what exists today.
Useful, but not required:
- What you want to achieve, in a sentence or two.
- Who the users are.
- What exists today: an app, a spreadsheet, a competitor you like.
- A budget range and a target date.
- Any documents, designs or links.
You do not need a pitch deck or a technical specification.