Latrīa is a Latin term (from the Greek λατρεία, latreia) used in Orthodox and Catholic theology to mean adoration, which is the highest form of worship or reverence and is directed only to the Holy Trinity.
Latria vs. Dulia and Hyperdulia
Latria is sacrificial in character, and may be offered only to God. Catholics offer other degrees of reverence to the Blessed Virgin Mary and to the Saints; these non-sacrificial types of reverence are called Hyperdulia and Dulia, respectively. Hyperdulia is essentially a heightened degree of dulia provided only to the Blessed Virgin. This distinction, written about as early as Augustine of Hippo and St Jerome, was detailed more explicitly by Thomas Aquinas in his Summa Theologiae, A.D. 1270, II II, 84, 1: "Reverence is due to God on account of His Excellence, which is communicated to certain creatures not in equal measure, but according to a measure of proportion; and so the reverence which we pay to God, and which belongs to latria, differs from the reverence which we pay to certain excellent creatures; this belongs to dulia, and we shall speak of it further on (II II 103 3)"; in this next article St. Thomas Aquinas writes: "Wherefore dulia, which pays due service to a human lord, is a distinct virtue from latria, which pays due service to the Lordship of God. It is, moreover, a species of observance, because by observance we honor all those who excel in dignity, while dulia properly speaking is the reverence of servants for their master, dulia being the Greek for servitude." From St. Thomas it is apparent that a clear distinction exists among latria and forms of dulia within Catholic theology.
Linguistic distinctions in English
Generally, in English, the word adoration is reserved for God alone and therefore it aptly translates latria. The word worship is a contraction of 'worth-ship' -- the state ("-ship") of being worthy -- and can be used in a strong sense in relation to God (latria), but also in a weak sense in relation to man: for instance, "His Worship the Mayor", or "Your Worship" (when addressing a magistrate in Court), or the worship of the saints (dulia) as distinct to the adoration of God (latria). Adoration provides a clear and unequivocal, and therefore better, translation of latria and expression of the absolute sacrificial reverence due to God alone.
"This worship called forth by God, and given exclusively to Him as God, is designated by the Greek name latreia (Latinized, latria), for which the best translation that our language affords is the word Adoration. Adoration is different from other acts of worship, such as supplication, confession of sin, etc., inasmuch as it formally consists in self-abasement before the Infinite, and in devout recognition of His transcendent excellence."Catholics, and Eastern Orthodox Christians especially adore with latria during their religious service, the Mass or Divine Liturgy. Other religious groups, such as Protestants and Muslims, do not have a Eucharistic sacrifice; Catholics consider that they literally participate in the sacrifice at the foot of Calvary, that what Christ offered once "participates in the divine eternity" (CCC § 1085), and thus have a very active sense of the worship of latria.
Some Protestants (some Methodists and Anglicans also venerate the Saints of both the Catholic, Orthodox and Anglican/Methodist Church) and others fault Catholic and Orthodox Christians for revering the Blessed Virgin Mary or the saints, declaring their distinction among latria, hyperdulia, and dulia to be hair-splitting, and furthermore reject Augustine, Jerome, Thomas Aquinas, and others as authorities. Protestantism considers the Catholic conception of the central religious service to be an error, arguing that the sacrifice of the Cross was unique (which Catholics also believe), and need not and should not be repeated, Heb 6:6, 9:25-28. Catholics counter this with verses such as Malachi 1:10-11 and by stating that they do not 'repeat' the Sacrifice of the Cross but they re-present it (make it present again). Protestantism also contends that the sacrificial aspect of Mass was unknown to the Primitive Church and is opposed to the Bible both in its general sense and specific instructions. The former assertion is a question of historical fact which Catholics answer with the writings of the early Christians and the Church Fathers; the latter is a matter of Scriptural interpretation, which Catholics contend is determined by the Church's Magisterium (bound by "Sacred Tradition"), and which most Protestants contend is determined solely by the Scripture (see: Sola Scriptura).