The Eucharist in the Catholic Church is the celebration of Mass, the eucharistic liturgy. The term Eucharist is also used for the bread and wine when transubstantiated (their substance having been changed), according to Catholic teaching, into the body and blood of Jesus Christ.
Blessed Sacrament is a devotional term used in the Roman Catholic Church to refer to the eucharistic species (the Body and Blood of Christ). Consecrated hosts are kept in a tabernacle after Mass, so that the Blessed Sacrament can be brought to the sick and dying outside the time of Mass. This makes possible also the practice of eucharistic adoration. Because Christ himself is present in the sacrament of the altar, he is to be honored with the worship of adoration. "To visit the Blessed Sacrament is ... a proof of gratitude, an expression of love,... and a duty of adoration toward Christ our Lord."