A Roman Catholic Mass celebrated in full ceremonial form, in which the celebrant is assisted by a deacon and a subdeacon and accompanied by acolytes, a thurifer, and a choir
main religious service in the Catholic Church (includes prayers, music, incense, etc.)
High mass is a church service held in a Catholic church in which there is more ceremony than in an ordinary mass. A Mass in which the celebrant is assisted by a deacon and a subdeacon and accompanied by acolytes, a thurifer, and a choir. a very formal church ceremony in the Roman Catholic Church