Host desecration

Host desecration is a form of sacrilege in Christianity (most frequently identified as such in the traditions of Anglicanism, Eastern and Oriental Orthodoxy, Lutheranism, Methodism, and Roman Catholicism) involving the mistreatment or malicious use of a consecrated host—the sacred bread used in the Eucharistic service of the Divine Liturgy or Mass. In Catholicism, where the host is held to have been transubstantiated into the body of Jesus Christ, host desecration is among the gravest of sins. Intentional host desecration is not only a mortal sin but also incurs the penalty of excommunication latae sententiae. Throughout history, a number of groups have been accused of desecrating the Eucharist, often with grave consequences due to the spiritual importance of the consecrated host.

Accusations against Jews were a common pretext for massacres and expulsions throughout the Middle Ages in Europe. Similar accusations were made in witchcraft trials; witch-hunter's guides such as the Malleus Maleficarum refer to hosts as being objects of desecration by witches. It is part of many descriptions of the Black Mass, both in ostensibly historical works and in fiction.

...
Wikipedia