Inclusive counting in the context of "Octave (liturgy)"

Pentecost (also called Whit Sunday, Whitsunday or Whitsun) is a Christian holiday that takes place on the 49th day (50th day when inclusive counting is used) after Easter. It commemorates the descent of the Holy Spirit upon the Apostles of Jesus, Mary, and other followers of the Christ, while they were in Jerusalem celebrating the Feast of Weeks, as described in the Acts of the Apostles (Acts 2:1–31). Pentecost marks the "Birthday of the Church".

Pentecost is one of the Great feasts in the Eastern Orthodox Church, a Solemnity in the Roman Rite of the Catholic Church, a Festival in the Lutheran Churches, and a Principal Feast in the Anglican Communion. Many Christian denominations provide a special liturgy for this holy celebration. Since its date depends on the date of Easter, Pentecost is a "moveable feast". The Monday after Pentecost is a legal holiday in many European, African and Caribbean countries.

The Roman calendar was the calendar used by the Roman Kingdom and Roman Republic. Although the term is primarily used for Rome's pre-Julian calendars, it is often used inclusively of the Julian calendar established by Julius Caesar in 46 BC.

According to most Roman accounts, their original calendar was established by their legendary first king Romulus. It consisted of ten months, beginning in spring with March and leaving winter as an unassigned span of days before the next year. These months each had 30 or 31 days and ran for 38 nundinal cycles, each forming a kind of eight-day week—nine days counted inclusively in the Roman manner—and ending with religious rituals and a public market. This fixed calendar bore traces of its origin as an observational lunar one. In particular, the most important days of each month—its kalends, nones, and ides—seem to have derived from the new moon, the first-quarter moon, and the full moon respectively. To a late date, the College of Pontiffs formally proclaimed each of these days on the Capitoline Hill and Roman dating counted down inclusively towards the next such day in any month. (For example, the year-end festival of Terminalia on 23 February was called VII. Kal. Mart., the 6th day before the March kalends.)

The Feast of the Ascension of Jesus Christ (also called the Solemnity of the Ascension of the Lord, Ascension Day, Ascension Thursday; or sometimes Holy Thursday, which can also mean the Thursday before Easter) commemorates the Christian belief of the bodily Ascension of Jesus into Heaven. It is one of the ecumenical (shared by multiple denominations) feasts of Christian churches, ranking with the feasts of the Passion and Pentecost. Following the account of Acts 1:3 that the risen Jesus appeared for 40 days prior to his Ascension, Ascension Day is traditionally celebrated on a Thursday, the fortieth day of Easter according to inclusive counting, although some Christian denominations have moved the observance to the following Sunday, sometimes called Ascension Sunday. The day of observance varies by ecclesiastical province in many Christian denominations, as with Lutherans and Catholics, for example.

Ascensiontide refers to the ten-day period between the Feast of the Ascension and the Feast of Pentecost. The Sunday within that period may be referred to as the Seventh Sunday of Easter or the Sunday in Ascensiontide.