Our English word “chant” comes from the Latin word cantus, which simply means “song.” So what we know as “chant” today is simply the form of singing that was used in the early church. However, the New Testament Christians didn't invent any music of their own. They primarily borrowed the style of singing used in the Jewish synagogue—which was what we know as chant.
Chant was organized and more fully developed during the time of Gregory the Great. That is why Christian chant is generally known today as Gregorian chant. However, Gregory did not invent the chant form. It was used by Christians centuries before him—and by the Jews before the time of Christ.
Unlike most music from ancient times, Christian chant has never died. It is a beautiful form of music—meditative, relaxing and peaceful—with a very other-worldly sound to it.