The Feast of Corpus Christi and Juliana of Liege

The Feast of Corpus Christi is a special celebration of the Eucharist - the Lord’s Supper- remembering the Holy Body and Blood of Christ.

It is liturgically celebrated on the Thursday after Trinity Sunday or*** where the Solemnity of the Holy Body and Blood of Christ is not a holy day of obligation, it is assigned to the Sunday after the Most Holy Trinity as its proper day.***

At the end of the Holy Mass there is a procession of the Blessed Sacrament generally displayed in a monstrance -an open or transparent receptacle in which the consecrated Host is displayed for veneration.

Corpus Christi wreaths, which are made of flowers, are hung on the doors and windows of the faithful in addition to being erected in gardens and fields.
The procession is followed by the Benediction of the Blessed Sacrament.
In Rome the Eucharistic procession is presided over by the Pope.
In Arundel, England, they have a central aisle of flower heads laid down in a colourful pattern.

The institution of Corpus Christi as a feast in the Christian Calender resulted from approximately 40 years of work on the part of Juliana of Liege, a 13th century Norbertine canoness.

Source
Wikipedia