From the Ramadan Wikipedia page:
Ramadan (also romanized as Ramazan, Ramadhan, or Ramathan) is the ninth month of the Islamic calendar, and is observed by Muslims worldwide as a month of fasting to commemorate the first revelation of the Quran to Muhammad according to Islamic belief. This annual observance is regarded as one of the Five Pillars of Islam. The month lasts 29–30 days based on the visual sightings of the crescent moon, according to numerous biographical accounts compiled in the hadiths.
The word Ramadan comes from the Arabic root ramiḍa or ar-ramaḍ, which means scorching heat or dryness. Fasting is fardh (obligatory) for adult Muslims, except those who are suffering from an illness, travelling, are elderly, pregnant, breastfeeding, diabetic or going through menstrual bleeding. Fasting the month of Ramadan was made obligatory (wājib) during the month of Sha'aban, in the second year after the Muslims migrated from Mecca to Medina. Fatwas have been issued declaring that Muslims who live in regions with a natural phenomenon such as the midnight sun or polar night should follow the timetable of Mecca.
While fasting from dawn until sunset, Muslims refrain from consuming food, drinking liquids, smoking, and engaging in sexual relations. Muslims are also instructed to refrain from sinful behavior that may negate the reward of fasting, such as false speech (insulting, backbiting, cursing, lying, etc.) and fighting. Food and drinks are served daily, before dawn and after sunset. Spiritual rewards (thawab) for fasting are also believed to be multiplied within the month of Ramadan. Fasting for Muslims during Ramadan typically includes the increased offering of salat (prayers) and recitation of the Quran.