Ecclesiastical Latin
Ecclesiastical Latin (also called Liturgical Latin or Church Latin) is the form of the Latin language used in the Roman Rite of the Catholic Church for liturgical and other purposes. It is distinguished from Classical Latin by some lexical variations, a simplified syntax and Italianate pronunciation.
The Ecclesiastical Latin used in theological works, liturgical rites and dogmatic proclamations varies in style: syntactically simple in the Vulgate Bible, hieratic in the Roman Canon of the Mass, terse and technical in Aquinas' Summa Theologica, and Ciceronian in Pope John Paul II's encyclical letter Fides et Ratio. Ecclesiastical Latin is the official language of the Holy See and the only surviving sociolect of spoken Latin.
Scope and usage
The Church issued the dogmatic definitions of the first seven General Councils in Greek, and even in Rome Greek remained at first the language of the liturgy and the language in which the first Popes wrote. During the Late Republic and Early Empire periods, educated Roman citizens were generally fluent in Greek, although state business was conducted in Latin.