Spousal privilege is a special privilege for married couples, which allows them to refuse to testify against their spouses without consent. It also allows them to not answer questions that would expose confidential marital communications. In other words, spousal privilege is a legal privilege that exists for married couples, which allows them to protect the privacy of their marriage, and to not have to speak against their spouse in court.
Spousal privilege only applies if the couple is still legally married during the period of the lawsuit. Also, spousal privilege does not apply to certain situations, such as divorce cases, cases that involve the children of the spouses, cases that involve one spouse causing harm to another, etc. The reason why spousal privilege exists is because the act of testifying against one's spouse could destroy many marriages. So, with a few exceptions, the court allows marital harmony to be preserved.