Christmas

Nativity of Our Lord
Joyous Celebration 25 December (Western); 7 January (Eastern Orthodox using Julian calendar) 1 day (liturgically); 12 days (Christmastide season)

Epiphany

Theophany
Joyous Celebration January 6 (Western); January 19 (Eastern Orthodox on Julian calendar) 1 day (concludes 12 days of Christmas; begins Epiphany season)

Islamic New Year

Hijri New Year
Commemorative 1 Muharram 1 day (month of Muharram sacred)

Ashura

Day of Ashura
Fast Day Muharram 10 1 day (Shia mourning extends through first 10 days)

Purim

Feast of Lots
Joyous Celebration Adar 14 (Adar II 14 in leap years); Shushan Purim on Adar 15 1-2 days

Passover

Pesach
Pilgrimage Festival Nisan 15-22 7-8 days (7 in Israel, 8 in diaspora)

Lent

Great Lent
Fast Day Ash Wednesday to Holy Saturday (40 days not counting Sundays) 40-46 days (varies by tradition)

Ash Wednesday

Day of Ashes
Fast Day 46 days before Easter (first day of Lent) 1 day (begins Lenten season)

Good Friday

Great Friday
High Holy Day Friday before Easter Sunday 1 day (part of Holy Week and Easter Triduum)

Easter

Pascha
High Holy Day First Sunday after first full moon following spring equinox 1 day (liturgically extends to 50 days until Pentecost)

Ramadan

Ramazan
Fast Day 9th month of Islamic calendar (Ramadan) 29-30 days (one lunar month)

Laylat al-Qadr

Night of Power
Commemorative One of last ten nights of Ramadan (odd nights, especially 27th Ramadan) 1 night (exact night unknown)

Eid al-Fitr

Festival of Breaking the Fast
Joyous Celebration Shawwal 1 (first day of month following Ramadan) 3 days of celebration (1 day required, 3 days customary)

Pentecost

Whitsunday
High Holy Day 50 days after Easter Sunday 1 day (liturgically extended to octave or season in some traditions)

Shavuot

Pentecost
Pilgrimage Festival Sivan 6 (50 days after Passover) 1-2 days (1 in Israel, 2 in diaspora)

Eid al-Adha

Festival of Sacrifice
Pilgrimage Festival Dhul Hijjah 10-13 (10th-13th of the 12th Islamic month) 4 days (Day of Arafah on 9th, then 4 days of Eid)

Tisha B'Av

Ninth of Av
Fast Day Av 9 1 day (25-hour fast)

Rosh Hashanah

Jewish New Year
High Holy Day Tishrei 1-2 2 days (1 day in biblical text; 2 days in rabbinic tradition)

Yom Kippur

Day of Atonement
High Holy Day Tishrei 10 25 hours (from sunset to nightfall next day)

Sukkot

Feast of Tabernacles
Pilgrimage Festival Tishrei 15-21 (22-23 in diaspora with Shemini Atzeret and Simchat Torah) 7 days (8-9 days including concluding festivals)

Advent

Adventus
Seasonal Four Sundays before Christmas (begins late November/early December) 4 weeks (approximately 22-28 days)

Hanukkah

Chanukah
Joyous Celebration Kislev 25 - Tevet 2 (or 3) 8 days

Mawlid an-Nabi

Mawlid al-Nabi
Commemorative Rabi' al-Awwal 12 (Sunni); Rabi' al-Awwal 17 (Shia) 1 day (often extended to full month of Rabi' al-Awwal)

All Saints' Day

All Hallows' Day
Commemorative November 1 (Western); First Sunday after Pentecost (Eastern Orthodox) 1 day

Ascension Day

Feast of the Ascension
Joyous Celebration 40 days after Easter (Thursday); some observe on 7th Sunday of Easter 1 day

Assumption of Mary

Feast of the Assumption
Joyous Celebration August 15 1 day

Baptism of the Lord

Commemorative Sunday after Epiphany (or January 13 in some traditions) 1 day

Hajj

The Pilgrimage
Pilgrimage Festival 8th-12th/13th Dhul-Hijjah 5-6 days

Maundy Thursday

Holy Thursday
High Holy Day Thursday before Easter 1 day (part of Easter Triduum)

Palm Sunday

Passion Sunday
Commemorative Sunday before Easter 1 day (begins Holy Week)

Shemini Atzeret

Eighth Day of Assembly
Pilgrimage Festival Tishri 22 1 day (2 days in diaspora)

Simchat Torah

Rejoicing in the Torah
Joyous Celebration Tishri 23 (Israel: Tishri 22) 1 day

Umrah

Lesser Pilgrimage
Pilgrimage Festival Any time of year (especially recommended in Ramadan) Varies (can be completed in a few hours)