The Liturgy of the Presanctified Gifts (Slavonic: Liturgija Preždeoscjaščénnych Darov) is a service unique to the Byzantine Rite. It is celebrated during the Great Fast, and provides the faithful with the opportunity to receive Holy Communion on those days when then the Eucharistic Sacrifice is not celebrated. The word "presanctified" indicates that the "gifts" (the Body and Blood of Christ) which are distributed at the service are those consecrated at a previous Eucharist.

Outline of the Service:

http://www.metropolitancantorinstitute.org/liturgy/DivineLiturgyPresanctifiedGifts.html