Express the business or system/project goals clearly and concisely. Give a brief overview of what problem the systems solves.

Detailed enough that readers of your (architecture) documentation can understand why the system exists and what its major/fundamental requirements are.

• Briefly explain the major (max 3-5) use-cases, features or functions.
• Document the top 3-5 quality requirements by showing scenarios (see question C-10-2 (quality scenarios)).
• Make sure the most important domain terms are commonly understood among the development team (arc42 provides a glossary section for that purpose, but you better let your product owner or other stakeholders create and maintain those definitions.)
• Link to additional requirements documentation, if it exists.