Responsorial

A responsory or respond is a type of chant in western Christian liturgies.

The most general definition of a responsory is any psalm, canticle, or other sacred musical work sung responsorially, that is, with a cantor or small group singing verses while the whole choir or congregation respond with a refrain. However, this article focuses on those chants of the western Christian tradition that have traditionally been designated by the term responsory. In the Roman Rite and rites strongly influenced by it, such as the pre-reformation English rite and the monastic rite of the Rule of St. Benedict, these chants ordinarily follow readings at services of the Divine Office (also called the Liturgy of the Hours); however, they have also been used as processional chants.

A responsory has two parts: a respond (or refrain), and a verse. Methods of performance vary, but typically the respond will be begun by the cantor then taken up by the entire choir. The verse is then sung by a cantor or a small group; or the verse can be begun by the cantor and continued by the entire choir. The chant concludes with a repetition of all or part of the respond. Sometimes the second repetition of the respond is followed by a half-doxology, Gloria Patri et Filio et Spiritui Sancto, sung by the cantor, followed in turn by a third repetition of all or part of the respond.

As an example, here is the responsory Aspiciebam, which in the Sarum Rite (the medieval rite of Salisbury Cathedral in England) followed the second reading, which was from the first chapter of the Book of Isaiah, at the night office (Matins) on the first Sunday of Advent:

Respond: (started by the cantor and continued by the whole choir) Aspiciebam in visu noctis, et ecce in nubibus caeli Filius hominis veniebat: et datum est ei regnum, et honor: * Et omnis populus, tribus, et linguae servient ei. (I saw in a night-vision, and behold, the Son of Man was coming on the clouds of heaven: and sovereignty and honor were given him: and every people and tribe, and all languages shall serve him.)

...
Wikipedia