When a husband and a wife speak to one another, their communications are protected by the marital privilege. This means that anything you say to your spouse must be kept confidential and cannot be disclosed in court (unless you want it to and your spouse agrees). This is intended to protect the sanctity of marital communications.
Similarly, communications with your attorney and with your doctor are also protected. But if you are speaking with your lawyer or your doctor and someone else is present, then generally the privilege is waived and communications can be compelled. For example, often in family law cases, clients will come in to speak to their lawyer with a supportive friend or family member. Often in these conferences, emotional issues are discussed. In addition, the tasks that need to be completed in your family law case can be overwhelming. Having someone there can help to understand what needs to be done. But you have to be careful when you do this, as the privilege between attorney and client is broken when someone else is present. This means that, if compelled by court, you would have to disclose what you talked about with your attorney at the meeting where your support person is present. This rarely comes up, but your attorney should be cautioning you when you come to a consultation appointment with a friend or family member.
In a recent case, Manela v. Superior Court (Manela), the court made a determination about when a privilege is waived in a somewhat unique situation. Mr. Manela was seeing his doctor with his wife, discussing a medical condition he had. When he got divorced, Mrs. Manela wanted to use the medical condition to discredit him, and Mr. Manela said the condition was protected by doctor-patient confidentiality as well as the marital communications privilege. The court said NO, that the privilege was waived when Mr. Manela spoke to his doctor with his wife present.
This is a good reminder about what is really confidential and what is not.