Introit

n.
  1. A going in.
  2. (R. C. Ch.) An anthem or psalm sung before the Communion service.
  3. Any composition of vocal music appropriate to the opening of church services.
    1. A psalm sung or chanted immediately before the collect, epistle, and gospel, and while the priest is entering within the rails of the altar.
    2. A part of a psalm or other portion of Scripture read by the priest at Mass immediately after ascending to the altar.