Why is It Called "Mass"?
There are some earlier examples, but it was in the sixteenth- and seventeenth-centuries that Catholics began to more frequently use the Latin word “Missa” for their eucharistic liturgies. Most think this is tied to the words that once dismissed the congregation: Ite, missa est, which means “go, it is sent.” The “it” is the Church ― the assembly of gathered Christians ― sent into the world. “Missa” is a “sending forth,” and it is from missa that we get the English word “Mass.”
The Mass being a “sending forth” shows its connection to evangelization, to the spread of Christianity. Christians are instructed to “go” out into the world. They are sent on “mission.” Indeed, “Mass” and “mission” share the same root. Today, one option for that final line of the Mass has been reworked to highlight this: “Go and announce the Gospel of the Lord.”