This doctrine is found in the Catechism of the Catholic Church, paragraphs 1030-1032:
"All who die in God's grace and friendship, but still imperfectly purified, are indeed assured of their eternal salvation; but after death they undergo purification, so as to achieve the holiness necessary to enter the joy of heaven. The Church gives the name Purgatory to this final purification of the elect, which is entirely different from the punishment of the damned...From the beginning the Church has honored the memory of the dead and offered prayers in suffrage for them, above all the Eucharistic sacrifice, so that, thus purified, they may attain the beatific vision of God. The Church also commends almsgiving, indulgences, and works of penance undertaken on behalf of the dead..."
- ℣. Requiem æternam dona ei (eis), Domine
- ℟. Et lux perpetua luceat ei (eis):
- ℣. Requiescat (-ant) in pace.
- ℟. Amen.
An English translation
The translation used by English-speaking Roman Catholics is:
- ℣. Eternal rest, grant unto him/her (them), O LORD,
- ℟. And let perpetual light shine upon him/her (them).
- ℣. May he/she (they) rest in peace.
- ℟. Amen.