Easter Triduum, Holy Triduum, or Paschal Triduum is the period of three days from Holy Thursday (seen as beginning with the service of the preceding evening) to Easter Sunday. It begins with the Thursday Mass of the Lord's Supper and ends with evening prayer on Sunday.
Since the 1955 reform by Pope Pius XII, the Easter Triduum, including as it does Easter Sunday, has been more clearly distinguished as a separate liturgical period. Previously, all these celebrations were advanced by more than twelve hours. The Mass of the Lord's Supper and the Easter Vigil were celebrated in the morning of Thursday and Saturday respectively, and Holy Week and Lent were seen as ending only on the approach of Easter Sunday.
After the Gloria in Excelsis Deo at the Mass of the Lord's Supper all church bells are silenced and the organ is not used. so that the period that lasted from Thursday morning to before Easter Sunday began was once, in Anglo-Saxon times, referred to as "the still days". 
In the Roman Catholic Church, weddings, which were once prohibited throughout the entire season of Lent and during certain other periods as well, are prohibited during the Triduum. Lutherans still discourage weddings during the entirety of Holy Week and the Triduum.
Mass of the Lord's Supper
- During the Gloria in Excelsis Deo, all church bells may be rung; afterwards, they are silenced until the Gloria of the Easter Vigil.
- After the homily of the Mass a ritual washing of the feet is envisaged.
- The Mass concludes with a procession of the Blessed Sacrament to the altar of repose..
- Eucharistic adoration is encouraged after this, but if continued after midnight should be done without outward solemnity..
- The liturgical colour for the Mass vestments and other ornaments is white.
- On Good Friday, Christians recall the Passion and crucifixion of Jesus.
- In the Roman, Lutheran, and High Anglican rites, a cross or crucifix (not necessarily the one which stands on or near the altar on other days of the year) is ceremoniously unveiled. (In pre-Vatican II services, other crucifixes were to be unveiled, without ceremony, after the Good Friday service.)
- In Roman Catholicism, the clergy traditionally begin the service prostrate in front of the altar. Mass is not celebrated on Good Friday and the communion distributed at the Celebration of the Lord's Passion is consecrated on Holy Thursday.
- Also in Roman Catholicism, images of saints are either kept or veiled until the Easter Vigil. Votive lights before these images are not lit. Crucifixes that are movable are hidden, while those that are not movable are veiled until the Easter Vigil.
- Only one cross or crucifix per church is unveiled throughout the entire Good Friday service, for the purpose of veneration by the congregation. Regardless of the size of the church or the congregation, it is not permissible to use two crucifixes for the said veneration. The faithful typically venerate the crucifix by kissing the feet of the corpus.
- Colors seen throughout the chapel or on vestments: Vary
- No color, red, or black are used in different traditions.
- Where colored hangings are removed for this day, liturgical color applies to vestments only.
- The priest wears red vestments, symbolic of the Blood of Jesus.
- A commemoration of the day that Jesus lay in his tomb.
- In the Roman Catholic Church, daytime Masses are never offered.
- There are no colors seen or used throughout the chapel or on vestments.
- Known as Black Saturday in the Philippines.
- Held after nightfall of Holy Saturday, or before dawn on Easter Sunday, in anticipation of the celebration of the resurrection of Jesus.
- The ceremony of darkness and light is held in silence at the beginning of the Mass.
- The paschal candle, representing Jesus's resurrection as the "return of light onto the world," is lit.
- The solemn procession to the altar with the Paschal candle is formed.
- Once everyone has processed in, the Exsultet is intoned.
- After the Exsultet, everyone is seated and listens to the 7 readings and 7 psalms, followed by the Epistle. These readings account salvation history, beginning with Creation.
- In pre- and post-Vatican II Roman Catholic practice, during the Gloria at the Mass, the organ and church bells are used in the liturgy for the first time in two days.
- If the lights of the Church have been previously left off, they are turned on as the Gloria begins
- A Solemn Alleluia is sung before the Gospel is read
- The Paschal candle is used to bless the baptismal font to be used by the Elect.
- The celebrant uses the term "Alleluia" for the first time since the beginning of Lent.
- People desiring to full initiation in the Church who have completed their training are formally initiated as members of the faith the Church through the Sacraments of Initiation (Baptism, confirmation, and the Holy Eucharist).
- In current Vatican II practice, the use of lighting to signify the emergence from sin and the resurrection of Jesus vary, from the use of candles held by parishioners as well as candelabras lit throughout the church.
- Statues of Jesus, which have been veiled during Passion (usually throughout Lent), are unveiled.
- Colors seen throughout the chapel or on vestments: White, often together with gold, with yellow and white flowers often in use in many parishes.
- The date of Easter varies from year to year, but is always on a Sunday between the dates of March 22 and April 25. It occurs on the first Sunday after the first full moon of Spring.
- The Easter octave allows for no other feasts to be celebrated or commemorated during it (possible exception is the Greater Litanies if Easter falls later in the year). If Easter is so early that March 25 falls in Easter week, the feast of the Annunciation is postponed to the following week.
- The Ascension is the fortieth day of Easter; which is always a Thursday. Pentecost (or Whitsun) is the fiftieth day.
- Easter Masses are held throughout the day and are similar in content to the Easter Vigil Mass. However, baptisms are not performed, and the ritual of the Paschal candle is not performed (the candle is placed next to the ambo, or podium, throughout the Easter celebration).
- The Easter season extends from the Easter Vigil through Pentecost Sunday on the Catholic and Protestant calendars, normally the fiftieth day after Easter. On the calendar used by traditional Catholics, Eastertide lasts until the end of the Octave of Pentecost, at None of the following Ember Saturday.
- The colors seen throughout the chapel or on vestments during the fifty-day Easter period are white or gold.
- ↑ 1.0 1.1 General Norms for the Liturgical Year and the Calendar, 19
- ↑ "Holy Week". Catholic Encyclopedia. New York: Robert Appleton Company. 1913. http://en.wikisource.org/wiki/Catholic_Encyclopedia_(1913)/Holy_Week.
- ↑ "Banns of Marriage". Catholic Encyclopedia. New York: Robert Appleton Company. 1913. http://en.wikisource.org/wiki/Catholic_Encyclopedia_(1913)/Banns_of_Marriage.
- ↑ Holy Thursday Evening Mass of the Lord's Supper, 44
- ↑ Holy Thursday Evening Mass of the Lord's Supper, 50
- ↑ Holy Thursday Evening Mass of the Lord's Supper, 51
- ↑ Holy Thursday Evening Mass of the Lord's Supper, 54
- ↑ Holy Thursday Evening Mass of the Lord's Supper, 56
- ↑ General Instruction of the Roman Missal, 346
- ↑ "Good Friday". Catholic Encyclopedia. New York: Robert Appleton Company. 1913. http://en.wikisource.org/wiki/Catholic_Encyclopedia_(1913)/Good_Friday.
- ↑ Catholic City Tenbrae Retrieved on April 5, 2007