Need to know is
(1) A rule by which individuals, processes, and systems are granted access to only the information, capabilities and assets which are necessary for execution of their authorized functions.
(2) A principle under which users, processes and systems are granted access to only the information, capabilities and assets which are necessary for execution of their authorized functions. 
Need-to-know: Refers to a need to access information based on an operational requirement. 
需要知道原則 : 需要知道原則是接達、知識或擁有執行公務所需的特定信息的 需要性。保安程序的需要知道原則，在於要求敏感訊息託管人 將透露訊息給別人之前，確保有適當的授權才能讓訊息接收者 接達訊息 。
Need-To-Know Principle: The necessity for access to, knowledge of, or possession of specific information required to carry out official duties. 
The need-to-know criterion is used in security procedures that require a custodian of sensitive information, prior to disclosing the information to someone else, to establish that the intended recipient has proper authorisation to access the information.
Necessità di conoscere: Principio che subordina l’accesso a determinate informazioni all’effettiva indispensabilità ai fini dello svolgimento di specifici compiti istituzionali. 
In materia di tutela della sicurezza delle informazioni, è una condizione aggiuntiva rispetto al possesso del Nulla Osta di Sicurezza per accedere ad informazioni con classifica superiore a riservato.
Need-to-know: een Vertrouwensfunctionaris mag slechts van Bijzondere Informatie kennisnemen als dat nodig is om zijn werk te kunnen doen. Bovendien mag hij deze kennis niet met collega’s delen voor wie deze kennis niet noodzakelijk is en/of geen vertrouwensfunctionaris zijn. 
Need To Know (NTK): The principle or policy of only allowing people access to data/information, equipment/devices and physical locations that is deemed necessary for them to know in order to carry out the task effectively. 
Need-to-know (NTK) is a method of isolating information resources based on a user's need to have access to that resource in order to perform their job but no more. 
The terms ‘need-to know” and “least privilege” express the same idea. Need-to-know is generally applied to people, while least privilege is generally applied to processes.
Need to know is a criterion used in security procedures that requires the custodians of classified information to establish, prior to disclosure, that the intended recipient must have access to the information to perform his or her official duties (source: JP 2-01.2)