noun, noun which may take the genitive case particle 'no'
confidential; personal; to be opened only by addressee
Used on envelopes or documents to indicate that the contents are private and should be opened only by the named recipient.
封筒に「親展」と書いてある。
The envelope is marked 'Confidential'.
親展の手紙が届いた。
I received a confidential letter.