Verb

1. Make sure all the field observations are classified by species.

Adjective

1. National security information formally assigned by governments 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.

   We do not discuss specific interrogation techniques because they are classified information.

2. Any information a person or organization does not wish to disclose.

   I won't say who I'm going to the prom with; that's classified.

Etymology 2

Noun

1. A classified advertisement in a newspaper or magazine.

   He ran a classified for the tools he wanted to sell.