A Host is a portion of bread used for Holy Communion in many Christian churches. In Western Christianity the host is often a thin, round unleavened wafer. The word 'host' is derived from the Latin hostia, which means 'sacrificial victim'. The term can be used to describe the bread both before and after consecration, though it is more correct to use it after consecration - "altar bread" being preferred before consecration. In the Catholic Church, at the Words of Institution the bread is changed or altered (known as transubstantiation) into the Body of Christ.
Hosts are often made by nuns as a means of supporting their religious communities. In the Latin Rite, unleavened bread is used as in the Jewish Passover or Feast of Unleavened Bread. The Byzantine Rite Eastern Catholic Churches (like the Eastern Orthodox Church) use leavened bread for Prosphora (the Greek word for Eucharistic altar bread). Some traditions proscribe the use of spiced, flavored or sweetened hosts, while others allow it. However, both Eastern and Western traditions insist that the bread must be made from wheat. The Code of Canon Law, Canon 924 requires that the hosts be made from wheat flour and water only.
The General Instruction of the Roman Missal §321 recommends that "the eucharistic bread ... be made in such a way that the priest at Mass with a congregation is able in practice to break it into parts for distribution to at least some of the faithful. ... The action of the fraction or breaking of bread, which gave its name to the Eucharist in apostolic times, will bring out more clearly the force and importance of the sign of unity of all in the one bread, and of the sign of charity by the fact that the one bread is distributed among the brothers and sisters."