What do Catholics believe takes place during Sacrificial Mass?

The language that is used to describe the Mass as a sacrifice is confusing to me, i. e. calling it "Sacrificial Mass." I understand that Catholics say that Jesus continually offers himself as a sacrifice before God for our sins. From Is the Mass a Sacrifice? : > He appears in heaven in the state of a victim not because he still needs to suffer but because for all eternity he re-presents himself to God appealing to the work of the cross, interceding for us (Rom 8:34), and bringing the graces of Calvary to us...So, the Mass is not repeating the murder of Jesus, but is taking part in what never ends: the offering of Christ to the Father for our sake What is happening during this offering? Why is is called "Sacrificial Mass" if no sacrifice is taking place but just a reference to the cross?