A response is the second half of one of a set of preces, the said or sung answer by a congregation or choir to a versicle said or sung by an officiant or cantor. In the following opening of the Anglican service of Morning Prayer according to the Book of Common Prayer (BCP), the first line is the versicle and the second is the response.
O: O Lord, open thou our lips P: And our mouth shall shew forth thy praise.In some liturgical books (such as hymnals or breviaries) the symbol "R/" or "℟" is used to denote a response.
There are many choral settings of the responses for BCP Evensong. Notable ones include those by Thomas Tomkins, William Smith, Richard Ayleward, Bernard Rose, and Humphrey Clucas.
References
Response (liturgy) Wikipedia(Text) CC BY-SA