noun
permit; license; written permission
Refers to a physical or official document granting permission, such as a permit or license.
このエリアで撮影するには許可書が必要です。
You need a permit to film in this area.
許可 is the general noun for permission or approval, while 許可書 specifically refers to the written document.
Compound of 許可 (permission) + 書 (document).