What is "invitatory"

Invitatory \In*vi"ta*to*ry\, a. [L. invitatorius: cf. F. invitatoire.] Using or containing invitations.

The ``Venite'' [Psalm xcv.], which is also called the invitatory psalm.
--Hook.

Invitatory \In*vi"ta*to*ry\, n.; pl. Invitatories. [LL. invitatorium: cf. F. invitatoire.] That which invites; specifically, the invitatory psalm, or a part of it used in worship.

a. Of or pertaining to an invitation n. (context music English) A psalm sung, as an invitation to prayer, at the beginning of some services

adj. conveying an invitation; "a brief invitatory note"

The Invitatory is the psalm used to start Nocturns in the Liturgy of the Hours, the Catholic Church's Divine Office. It is usually Psalm 94(95), which begins Venite exsultemus in Latin. After the reform of the Liturgy of the Hours following the Second Vatican Council, the Invitatory is said either before the Office of Readings or Lauds, whichever is said first in a liturgical day. In place of Psalm 94(95), Psalm 99(100), Psalm 66(67), or Psalm 23(24) may be used as circumstances may suggest.

Verse 15 of Psalm 50(51) is often used as the invitatory antiphon in the Liturgy of the Hours.