Sawm الصوم or Siyam الصيام is the Arabic word for fasting.
Muslims are prohibited from eating, drinking, smoking, and engaging in sexual intercourse from dawn (fajr) to sunset (maghrib) while fasting.
Fasting is essentially an attempt to seek nearness to Allah and increase one's piety. One of the remote aims of fasting is to empathize with those less fortunate ones who do not always have food and drink readily available. Also one must try to avoid cursing and thinking evil thoughts. Fasting is also viewed as a means of controlling one's desires (of hunger, thirst, sexuality, anger) and focusing more on devoting oneself to God.
Sawm also carries a significant spiritual meaning. It teaches one the principle of love: because when one observes fasting, it is done out of deep love for God and to learn self-restraint.