I started jotting down some notes and references about the traditional form of the Mass in response to a young friend of mine, Dana Cash, who I met as a fellow Israel pilgrim in 2004. Dana is somehow connected to a group called Una Voce and somehow involved in the creation of a website for the Tridentine Mass.
The correct term for this type of Mass is the extraordinary form. Pope Benedict XVI gave this name to the form in his Apostolic Letter on the subject of the liturgy, a Motu Proprio called Summorum Pontificum. (The term Motu Proprio means "on his own initiative.")
The pope stated that the form of the Mass found in the Roman Missal of Pope Paul the VI (1970) is the ordinary form of the Mass.
The ordinary form is referred to elsewhere as the Novus Ordo, and it was followed almost exclusively for years after Pope Paul VI promulgated it after Vatican II. The Novus Ordo form is a much altered form of the traditional Mass that is said in the vernacular (which is the native tongue of the land in which it is said). According to the above-mentioned Motu Proprio, "Vatican Council II expressed a desire that the respectful reverence due to divine worship should be renewed and adapted to the needs of our time."
Some believed that the earlier form of the Mass which was last defined in the Roman Missal published by Bl. Pope John XXIII had been forbidden. But, as the Pope wrote in a letter that accompanied the Motu Proprio, it never was. "There is no contradiction between the two editions of the Roman Missal. In the history of the liturgy there is growth and progress, but no rupture. What earlier generations held as sacred, remains sacred and great for us too, and it cannot be all of a sudden entirely forbidden or even considered harmful."
In the Motu Proprio, the Pope defined the form of the Roman rite said according to the missal of Pope John XXIII from 1962 as the extraordinary form. It is said in Latin, but it was changed significantly from the Tridentine rite. See good definition. It is also sometimes referred to as the "usus antiquor."