The phrase "between you, me, and the bedpost" is an idiom that refers to information that is shared between two people and should be kept confidential. There are several other synonyms for this phrase, including "off the record," "in confidence," and "just between us." Additionally, people may use the phrase "under wraps," "behind closed doors," or "quiet as a mouse" to indicate that the information being shared should not be broadcast widely. Regardless of the wording used, it is essential to understand the importance of keeping confidential information private and to only share it with those who have a need to know.