The Holy Week- Holy Thursday

Holy Week is the week before the great celebration of the Resurrection of Christ on Easter Sunday. It also commemorates the Passion of Christ and Death of Christ. 

In most countries, Holy Thursday is the start of the national holiday in observance of the Holy Week. It celebrates both the institution by Christ himself of the Eucharist and of the institution of the sacerdotal priesthood (as distinct from the 'priesthood of all believers') for in this, His last supper with the disciples, a celebration of Passover, He is the self-offered Passover Victim, and every ordained priest to this day presents this same sacrifice, by Christ's authority and command, in exactly the same way. The Last Supper was also Christ's farewell to His assembled disciples, some of whom would betray, desert or deny Him before the sun rose again.

On Holy Thursday a special mass in Cathedral Churches is celebrated, with as many priests of the diocese that can attend, this is because this day is a solemn observance of Christ's institution of priesthood. There's a 'Chrism Mass' in which the bishop blesses the Oil of Chrism used for Baptism and Confirmation. The bishop then washes the feet of twelve of the priests, to symbolize Christ's washing the feet of his Apostles, the first priests. Then  the Last Supper

Maundy Thursday also gives emphasis on the ancient tradition of spring cleaning, evidently related to the Jewish custom of ritually cleaning the home in preparation for the Feast of Passover. Everything was to be cleaned and polished in preparation for the Easter celebration. It was because of the "cleaning" that it was called Maundy Thursday.

Source: Catholic.org