Translated from Latin, Corpus Domini literally means "The Body of the Lord" or "The Body of Christ." Corpus Christi is essentially a celebration of the death and resurrection of Jesus Christ and observation of the Holy Eucharist; it is known as the Feast of Corpus Christi (the Feast of the Body and Blood of Christ), or the Solemnity of the Most Holy Body and Blood of Christ. As a holiday, it is celebrated predominantly by the Roman Catholic and the Anglican Church on the Thursday after Trinity Sunday—sixty days after Easter (usually between late May and the mid-June).
Corpus Christi was proclaimed on August 11, 1264, by Pope Urban IV, whose papal Bull ("Transiturus de hoc mundo") defines the purpose of the Solemnity of Corpus Christi and orders the Feast to be celebrated as an annual holiday; the liturgy for the Feast was written by Thomas Aquinas.
Pope Urban IV was inspired by the visions of St. Juliana of Mont Cornillon in Belgium—a nun who was told by Christ that the Holy Eucharist should be celebrated by establishing a liturgical feast in honor of the Blessed Sacrament; he was also impressed by the miracle known as the Eucharistic miracle at Bolsena (1263), in which a German priest, who stopped in Bolsena, Italy, to celebrate Mass witnessed a consecrated host bleeding after the prayer was finished, indicating that Jesus is present in the Eucharist.
This year, Corpus Domini or Corpus Christi is on June 3, 2021.