What Exactly is Sacred Music?

The phrase “sacred music” has gained a lot of traction in Catholic conversations in recent years, with many liturgists and other Church leaders emphasizing the importance of “sacred music” in the Church’s liturgies. But to the average Catholic in the pew - even one who attends weekly Mass and takes his or her faith life seriously - the meaning of the phrase may not immediately be clear. What makes music “sacred”? Must it be in Latin? Chanted? Accompanied by an organ? Can any music be sacred if it is intended for use in the liturgy? And why does it matter what music gets played at Mass?