This day, Maundy Thursday (also "Holy Thursday" or "Shire Thursday"1) commemorates Christ's Last Supper and the initiation of the Eucharist. Its name of "Maundy" comes from the Latin word mandatum, meaning "command." This stems from Christ's words in John 13:34, "A new commandment I give unto you." It is the first of the three days known as the "Triduum," and after the Vigil tonight, and until the Vigil of Easter, a more profoundly somber attitude prevails (most especially during the hours between Noon and 3:00 PM on Good Friday). Raucous amusements should be set aside...
The Last Supper took place in "the upper room" of the house believed to have been owned by John Mark and his mother, Mary (Acts 12:12). This room, also the site of the Pentecost, is known as the "Coenaculum" or the "Cenacle" and is referred to as "Holy and glorious Sion, mother of all churches" in St. James' Liturgy. At the site of this place -- our first Christian church -- a basilica was built in the 4th century. It was destroyed by Muslims and later re-built by the Crusaders. Underneath the place is the tomb of David.
After the Supper, He went outside the Old City of Jerusalem, crossed the Kidron Valley, and came to the Garden of Gethsemani, a place whose name means "Olive Press," and where olives still grow today. There He suffered in three ineffable ways: He knew exactly what would befall Him physically and mentally -- every stroke, every thorn in the crown He would wear, every labored breath He would try to take while hanging on the Cross, the pain in each glance at His mother; He knew that He was taking on all the sins of the world -- all the sins that had ever been or ever will be committed; and, finally, He knew that, for some people, this Sacrifice would not be fruitful because they would reject Him. Here He was let down by His Apostles when they fell asleep instead of keeping watch, here is where He was further betrayed by Judas with a kiss, and where He was siezed by "a great multitude with swords and clubs, sent from the chief Priests and the ancients of the people" and taken before Caiphas, the high priest, where he was accused of blasphemy, beaten, spat upon, and prepared to be taken to Pontius Pilate tomorrow morning.
As for today's liturgies, in the morning, the local Bishop will offer a special Chrism Mass during which blesses the oils used in Baptism, Confirmation, Holy Orders, Unction, and the consecration of Altars and churches.
At the evening Mass, after the bells ring during the Gloria, they are rung no more until the Easter Vigil (a wooden clapper called a "crotalus" is used insead). Parents explain this to their children by saying that the all the bells fly to Rome after the Gloria of the Mass on Maundy Thursday to visit the Popes. Children are told that the bells sleep on the roof of St. Peter's Basilica, and, bringing Easter eggs with them, start their flight home at the Gloria at the Easter Vigil, when when they peal wildly.
Then comes the Washing of the Feet after the homily, a rite performed by Christ upon His disciples to prepare them for the priesthood and the marriage banquet they will offer, and which is rooted in the Old Testament practice of foot-washing in preparation for the marital embrace (II Kings 11:8-11, Canticles 5:3) and in the ritual ablutions performed by the High Priest of the Old Covenant (contrast Leviticus 16:23-24 with John 13:3-5). The priest girds himself with a cloth and washes the feet of 12 men he's chosen to represent the Apostles for the ceremony.
The rest of the Mass after the Washing of the Feet has a special form, unlike all other Masses. After the Mass, the priest takes off his chasuble and vests in a white cope. He returns to the Altar, incenses the Sacred Hosts in the ciborium, and, preceded by the Crucifer and torchbearers, carries the Ciborium to the "Altar of Repose," also called the "Holy Sepulchre," where it will remain "entombed" until the Mass of the Presanctified on Good Friday.
Then there follows the Stripping of the Altars, during which everything is removed as Antiphons and Psalms are recited. All the glorious symbols of Christ's Presence are removed to give us the sense of His entering most fully into His Passion. Christ enters the Garden of Gethsemani; His arrest is imminent. The joyful signs of His Presence won't return until Easter begins with the Easter Vigil Mass on Saturday evening.
And, of course, tomorrow's Matins and Lauds may be read as part of the "tenebrae service" (see Spy Wednesday).
As to customs, many families have a practice of visiting the tabernacles of three or seven nearby churches after the Mass on this day as a sort of "mini-pilgrimage" (any nearby Catholic churches will do). Some families visit the churches directly after the evening Mass; others go home and wake up in the middle of the night to make the visits (though since churches are rarely open all night these days, this would be hard to do). The spirit of the visits to the churches is keeping vigil in the Garden of Gethsemani while Jesus prayed before His arrest. Matthew 26:36 "Then Jesus came with them into a country place which is called Gethsemani; and he said to his disciples: Sit you here, till I go yonder and pray."
In Germany, Maundy Thursday is known as "Green Thursday" (Grundonnerstag), and the traditional foods are green vegetables and green salad, especially a spinach salad. In Latin countries, Jordan almonds ("confetti") are eaten today and also throughout Eastertide.
Back when Kings and Queens of England were Catholic, they, too, would wash the feet of 12 subjects, seeing the footwashing rite also as an example of service and humility. They would also give money to the poor on this day, a practice is said to have begun with St. Augustine of Canterbury in A.D. 597, and performed by Kings since Edward II. Now the footwashing isn't done (it was given up in the 18th c.), but a special coin called "Maundy Money" is minted and given to the selected elderly of a representative town.
On this day, one may gain a plenary indulgence, under the usual conditions, by reciting the Tantum Ergo (Down in Adoration Falling).
1 The name "Shire Thursday" is explained in "Festival" printed by Wynkyn de Worde in 1511: "Yf a man aske why Shere Thursday is called so, ye may saye that in Holy Churche it is called (Cena Domini) our Lordes Souper daye; for that day he souped with this Discyples openly; and after souper he gave them his flesshe and his blode to ete and drynke. It is also in Englysshe called Sher Thursdaye, for in olde faders dayes the people wold that daye sher there heedes, and clyppe theyr berdes, and poll theyr heedes, and so make them honest ayenst Ester Day."