Introit

1. often capitalized : the first part of the traditional proper of the Mass consisting of an antiphon, verse from a psalm, and the Gloria Patri. 2. : a piece of music sung or played at the beginning of a worship service.

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, which are spoken or sung at the beginning of the celebration.

The Introit (Introitus) of the Mass is the fragment of a psalm with its antiphon sung while the celebrant and ministers enter the church and approach the altar. In all Western rites the Mass began with such a processional psalm since the earliest times of which we have any record.

The Introit is a processional chant that was originally a psalm with a refrain sung between verses. By the 9th century it had received its present form: refrain in a neumatic style - a psalm verse in psalm-tone style - refrain repeated. The Gradual, introduced in the 4th century, also…

In the broader sense, it's a short choral piece sung at the beginning of a worship service. In the capital-I sense, an Introit is a specific opening section of the Roman Catholic Mass. For the church where I minister, an introit needs to have these characteristics: fairly short (around one minute long)

There is a unique introit with its own proper text for each Sunday and feast day of the Roman liturgy. The introit is essentially an antiphon or refrain sung by a choir, with psalm verses sung by one or more cantors or by the entire choir.

Roman Catholic Church. a part of a psalm with antiphon recited by the celebrant of the Mass at the foot of the altar and, at High Mass, sung by the choir when the priest begins the Mass. Anglican Church, Lutheran Church.