change-of-address notice
A formal notice sent to inform others of one's new address after moving.
I submitted a change-of-address notice to the post office.
Please don't forget to send a change-of-address notice.
転居届 is a more general term for a change-of-address notification, while 転居通知 often refers to a specific notice sent to post offices or services.
Compound of 転居 (change of residence) and 通知 (notice).