Ramadan is the holy month of fasting for Muslims. Ramadan falls during the ninth month of the lunar calendar, which often falls sometime during November on the Western calendar. It is not a U.S. federal holiday. Muslims believe that the Koran, the Muslim holy book, was revealed to the prophet Muhammad during Ramadan. During Ramadan, Muslims celebrate the revelation of the Koran to Muhammad. Throughout the entire month, devout adult Muslims fast, or refrain from eating or drinking, from sunup to sundown. Muslims believe fasting purifies their bodies and spirit and increases their devotion to Allah (God). Worship and charity is considered very important during Ramadan. Muslims pray and recite the Koran during Ramadan. At the end of Ramadan, Muslims gather to pray together, often in mosques, greet family, friends, and neighbors, and celebrate with feasts. It is also considered important to offer charity to the poor.