Ramadan is the ninth month of the Islamic calendar which is based on the lunar system. Muslims fast for 29/30 days by abstaining from food, drink, nourishment and sexual relations from dawn to sunset. Fasting is the fourth pillar of Islam and it is an obligation upon all Muslims, who have reached puberty. However, certain people such as the ill or frail; pregnant and menstruating women; breast feeding mothers, children and travellers are exempt from fasting. They are allowed to defer their fasts until a later date, or if they are unable to fast they are required to give a determined sum to charity. Muslims begin their fast at dawn with a meal known as Suhoor and break their fast at sunset with a meal known as Iftar.