The Introit (from Latin: introitus, "entrance") is part of the opening of the liturgical celebration of the Eucharist for many Christian denominations. In its most complete version, it consists of an antiphon, psalm verse and Gloria Patri that is spoken or sung at the beginning of the celebration. It is part of the Proper of the liturgy; that is, the part that changes over the liturgical year.
In the Roman Rite of the Roman Catholic Church it is known as the antiphona ad introitum (Entrance antiphon), as in the text for each day's Mass, or as the cantus ad introitum (Entrance chant) as in the General Instruction of the Roman Missal, 47 and as in the First Roman Ordo (sixth to seventh century). In pre-1970 editions of the Roman Missal, the word Introitus was used, distinguished from the normal meaning of the word (entrance) by being capitalized. In Ambrosian chant and Beneventan chant, the counterpart of the Introit is called the "ingressa". In the Mozarabic, Carthusian, Dominican, and Carmelite Rites, it is called the "officium".
n. 1 The action of entering or going in; an entrance. 2 (context figuratively obsolete English) An introduction. 3 (context Roman Catholicism English) A psalm sung or chanted immediately before the collect, epistle, and gospel, and while the priest is entering within the rails of the altar, which begins with this verse: ''«Requiem aeternam dona eis, Domine»''. 4 (context Roman Catholicism English) A part of a psalm or other portion of Scripture read by the priest at Mass immediately after ascending to the altar. 5 An anthem or psalm sung before the Communion service. 6 Any composition of vocal music appropriate to the opening of church services.
The Collaborative International Dictionary
Introit \In*tro"it\, n. [L. introitus, fr. introire to go into, to enter; intro within + ire to go: cf. F. introit.]
A going in.
(R. C. Ch.)
A psalm sung or chanted immediately before the collect, epistle, and gospel, and while the priest is entering within the rails of the altar.
A part of a psalm or other portion of Scripture read by the priest at Mass immediately after ascending to the altar.
(R. C. Ch.) An anthem or psalm sung before the Communion service.
Any composition of vocal music appropriate to the opening of church services.
Douglas Harper's Etymology Dictionary
Usage examples of "introit".
Gregorian chants, intoned and mumbled Introits, Kyries, heard and unheard consecrations.
On the epistle side now, the Introit, Kyrie, and Gloria concluded.
Immediately after the prayers at the foot of the altar -- Father Gusewski stood on the Epistle side and was busy with the Introit -- I sighted him in the second pew, before the altar of Our Lady.
And Amsel lifted it up, counted the remaining fabric-covered buttons, tested every rent with parted fingers, demonstrated what a shepherd's incited fangs can do, and after this instructive Introit, proceeded to the Mass: he ogled through jagged holes, peered through slits, widened burst seams with two malignant fingers, was wind under coattails, finally crawled in, became entirely one with the festive tatter, transubstantiated himself and the cloth, and treated the audience to a performance featuring a disabled swallowtail coat: Amsel looked terrifying.