Under wrap is often used as an idiom to indicate something that is hidden or confidential. While this phrase is more commonly used in casual conversation, there are many other idiomatic expressions that can be used instead of under wrap. Some of these include "under lock and key," "behind closed doors," "in the vault," "hush-hush," "top secret," and "confidential." These phrases all lend an air of secrecy and exclusivity to the subject matter being discussed, and can be useful when describing sensitive information or maintaining confidentiality.