保密性（secrecy），又称机密性，一般称秘密，是指个人或团体的信息不为其他不应获得者获得。在电脑中，许多软件包括邮件软件、网络浏览器等，都有保密性相关的设置，用以维护用户信息的保密性，另外木马软件或骇客有可能会造成保密性的问题。

Secrecy (also called clandestinity or furtiveness) is the practice of hiding information from certain individuals or groups who do not have the "need to know", perhaps while sharing it with other individuals. That which is kept hidden is known as the secret.