What is the Mass?

According to the Council of Trent Sesson XXII, Chapter II:

''That the Sacrifice of the Mass is propitiatory both for the living and the dead.

And forasmuch as, in this divine sacrifice which is celebrated in the mass, that same Christ is contained and immolated in an unbloody manner, who once offered Himself in a bloody manner on the altar of the cross; the holy Synod teaches, that this sacrifice is truly propritiatory and that by means thereof this is effected, that we obtain mercy, and find grace in seasonable aid, if we draw nigh unto God, contrite and penitent, with a sincere heart and upright faith, with fear and reverence. For the Lord, appeased by the oblation thereof, and granting the grace and gift of penitence, forgives even heinous crimes and sins. For the victim is one and the same, the same now offering by the ministry of priests, who then offered Himself on the cross, the manner alone of offering being different. The fruits indeed of which oblation, of that bloody one to wit, are received most plentifully through this unbloody one; so far is this (latter) from derogating in any way from that (former oblation). Wherefore, not only for the sins, punishments, satisfactions, and other necessities of the faithful who are living, but also for those who are departed in Christ, and who are not as yet fully purified, is it rightly offered, agreebly to a tradition of the apostles.''