What is the meaning of Classified?

simple past and past participle of classify

Sorted into classes or categories.

Formally assigned by a government to one of several levels of sensitivity, usually (in English) top secret, secret, confidential, and, in some countries, restricted; thereby making disclosure to unauthorized persons illegal.

Not meant to be disclosed by a person or organization.

A classified advertisement in a newspaper or magazine.

Source: wiktionary.org