Wikipedia is never a bad place to start ...

Ramadan (Arabic: رمضان, Ramaḍān) is a Muslim religious observance that takes place during the ninth month of the Islamic calendar, believed to be the month in which the Qur'an was revealed to Angel Gabriel which later was revealed to Prophet Muhammad. It is the Islamic month of fasting (sawm), in which participating Muslims do not eat or drink anything from dawn until sunset. Fasting is meant to teach the person patience and humility. Ramadan is a time to fast for the sake of God, and to offer even more prayer than usual. Also involved in Ramadan are asking forgiveness for the sins of the past, asking for guidance in the future, and asking for help with refraining from every day evils and trying to purify oneself through self-restraint and good deeds.