Great Lent, or the Great Fast, is the most important fasting season in the church year in Eastern Christianity, which prepares Christians for the greatest feast of the church year, Pascha (Easter). In many ways Great Lent is similar to Lent in Western Christianity. There are some differences in the timing of Lent (besides calculating the date of Easter) and how it is practiced, both liturgically in the public worship of the church and individually.

One difference between Eastern Christianity and Western Christianity is the calculation of the date of Easter (see Computus). Most years, the Eastern Pascha falls after the Western Easter, and it may be as much as five weeks later; occasionally, the two dates coincide. Like Western Lent, Great Lent itself lasts for forty days, but unlike the West, Sundays are included in the count. Great Lent officially begins on Clean Monday, seven weeks before Pascha (Ash Wednesday is not observed in Eastern Christianity) and runs for 40 contiguous days, concluding with the Presanctified Liturgy on Friday of the Sixth Week. The next day is called Lazarus Saturday, the day before Palm Sunday. However, fasting continues throughout the following week, known as Passion Week or Holy Week, and does not end until after the Paschal Vigil early in the morning of Pascha (Easter Sunday).

Ramadan (Arabic: رمضان‎ Ramaḍān, IPA: [rɑmɑˈdˤɑːn]; ^variationsPersian: Ramazan‎) is the ninth month of the Islamic calendar, which lasts 29 or 30 days. It is the Islamic month of fasting, in which participating Muslims refrain from eating, drinking, smoking and sex during daylight hours and is intended to teach Muslims about patience, spirituality, humility and submissiveness to God. Muslims fast for the sake of God (Arabic: الله‎, trans: Allah) and to offer more prayer than usual. Compared to the solar calendar, the dates of Ramadan vary, moving backwards by about eleven days each year depending on the moon; thus, a person will have fasted every day of the Gregorian calendar year in 34 years' time. Muslims believe Ramadan to be an auspicious month for the revelations of God to humankind, being the month in which the first verses of the Qur'an were revealed to the Islamic prophet, Muhammad.

The word Ramadan is derived from an Arabic root R-M-Ḍ, as in words like "ramiḍa" or "ar-ramaḍ" denoting intense heat, scorched ground and shortness of rations. Ramadan, as a name for the month, is of Islamic origin. Prior to Islam and the exclusion of intercalary days from the Islamic calendar, the name of the month was Natiq and the month fell in the warm season.^[2] The word was thus chosen as it well represented the original climate of the month and the physiological conditions precipitated from fasting. In the Qur'an, God proclaims that "fasting has been written down (as obligatory) upon you, as it was upon those before you". According to a hadith, this might refer to the Jewish practice of fasting on Yom Kippur.^[3][4]