Today is Corpus Christi Sunday (Corpus Christi is Latin for Body of Christ), the solemn commemoration of the institution of the Eucharist. It s an act of homage and gratitude to Christ, who by instituting the Holy Eucharist gave to the Church her greatest treasure. Holy Thursday, assuredly, marks the anniversary of the institution, but the commemoration of the Lord’s Passion that very night suppresses the rejoicing proper to the occasion. Today’s observance, therefore, accents the joyous aspect of Holy Thursday.
Note that the feast is liturgically celebrated on the Thursday after Trinity Sunday (which was last Thursday), but where it isn’t observed as a holy day, like in Canada and USA, it is assigned to the Sunday after Trinity Sunday. A lot of communities hold Eucharistic processions on this feast. A notable Eucharistic procession is the one presided by the Pope each year in Rome where it begins at the Archbasilica of St John Lateran and makes its way to the Basilica of Saint Mary Major where it concludes with the Benediction of the Blessed Sacrament.
The liturgical solemnity of Corpus Christi celebrates the tradition and belief in the Body and Blood of Christ and his Real Presence in the Euchrist.