Saum means ‘fasting’. Saum is one of the five pillars of Islam and obligatory for Muslims in the month of Ramadan. Outside of Ramadan, voluntary or nawafil fasts can be observed on any day of the year except for some prohibited days. Saum starts at the time of dawn, after having the morning meal, or suhoor. It is broken by having iftaar, or breakfast at sunset.
While fasting, Muslims must abstain from drinking, eating, smoking, and having sexual intercourse. Although it is obligatory for Muslims to observe fasting during Ramadan, they may be exempt in some cases, like when ill, or traveling. Such people may have to make their missed fasts later on in the year.