Definition of "Confidential" :

adjective: the level of official classification for documents next above restricted and below secret; available only to persons authorized to see documents so classified

adjective: denoting confidence or intimacy

"A confidential approach."

adjective: (of information) given in confidence or in secret

"This arrangement must be kept confidential."

adjective: entrusted with private information and the confidence of another

"A confidential secretary."