noun
address supplement; additional address info
Refers to extra details like building name, apartment number, or room number that help identify a specific location within a larger address.
住所の後ろに方書としてマンション名と部屋番号を書いてください。
Please write the apartment name and room number as additional address information after the address.
この方書がないと、配達員が迷ってしまうかもしれません。
Without this address supplement, the delivery person might get lost.
住所 is the main address; 方書 is the extra detail that pinpoints the exact spot within that address.
Compound of 方 (かた, direction/person) and 書 (がき, writing), literally 'direction writing', referring to supplementary address details.