The eucharistic Divine Liturgy is not celebrated in the Orthodox Church on lenten weekdays. In order for the faithful to sustain their lenten effort by participation in Holy Communion, the Liturgy of the Presanctified Gifts is served. The service is an ancient one in the Orthodox Church. We officially hear about it in the canons of the seventh century, which obviously indicates its development at a much earlier date.

On all days of the holy fast of Lent, except on the Sabbath, the Lord’s Day, and the holy day of the Annunciation, the Liturgy of the Presanctified is to be served (Canon 52, Quinisext, 692).

The Liturgy of the Presanctified Gifts is an evening service. It is the solemn lenten Vespers with the administration of Holy Communion added to it. There is no consecration of the eucharistic gifts at the presanctified liturgy. Holy Communion is given from the eucharistic gifts sanctified on the previous Sunday at the celebration of the Divine Liturgy, unless, of course, the feast of the Annunciation should intervene; hence its name of “presanctified.”

https://oca.org/orthodoxy/the-orthodox-faith/worship/the-church-year/liturgy-of-the-presanctified-gifts