1. not written down or recorded in writing
2. understood or accepted but not formally stated or recorded

Examples

• The tribe’s history was passed down through unwritten traditions.
• There’s an unwritten rule that you don’t sit in someone else’s usual spot.
• The agreement was based on unwritten understandings between the parties.
• Many social customs are unwritten but widely followed.
• The company has several unwritten policies about dress code.
• Unwritten laws of hospitality guided their behavior toward guests.