9th Month of the Muslim Calendar.
Based on a lunar calendar and therefore varies every year.

The Holy Month of Ramadan is a time when Muslims fast during daylight hours to celebrate the time when Allah revealed the first verses of the Qu’ran, the holy book of Islam.
It is a time for spiritual reflection, prayer, doing good deeds, charity, spending time with loved ones. It teaches self-discipline, self-restraint, generosity and understanding of those less fortunate.

Note that in the Muslim calander, a holiday begins on the sunset of the previous day, so observing Muslims will celebrate Ramadan on the sunset of the day before.

Although Ramadan is always on the same day of the Islamic calendar, the date on the Gregorian calendar varies from year to year, since the Gregorian calendar is a solar calendar and the Islamic calendar is a lunar calendar. This difference means Ramadan moves in the Gregorian calendar approximately 11 days every year. The date of Ramadan may also vary from country to country depending on whether the moon has been sighted or not.