Fasting, or Siyaam, has two meanings. Generally, Siyaam, or Sawm, is derived from the root Sama, to restrain from normal things, such as eating, drinking, and talking. If an individual refrains from these things, he is considered saaim, the observer of fast. Al-Qur'an uses the word generally when it reveals the conversation between the angel and Maryam (Radiallahuanha), the mother of Prophet Isa (alaihissalam), as the angel instructed her: "...And if you do see any man, say, 'I have vowed to remain silent for Allah.'" (Al-Qur'an 19:26)
The phrase "to remain silent" is the interpretation of the Arabic word, "sawm." The reason for this interpretation is that "sawm" cannot mean fast, i.e. restraint from food, because Maryam (Radiallahuanha) had just been told to eat from the palm tree. This general meaning is common in the Arabic language.
In the Shari'ah, Islamic law, the word "Sawm" means and implies a specific act, that, is, "to worship Allah, abstaining, to please Him from fast breakers, such as physical nourishment, food, drink, and sexual intercourse or a lustful discharge of semen from the period between the break of dawn until sundown.
As this definition implies, Islamic fasting is total abstinence from any food particles passing through the mouth or nose, as well as drinks of any kind - water, milk, juices, etc. - along with abstinence from sexual association during the day that commences from the break of dawn till sunset.
Although the definition indicates restraining the stomach and private parts, the tongue, eyes, ears, and other limbs are equally obligated to be restrained if the faster wants to gain the total rewards of fasting. This is why the Messenger of Allah (saas) has been reported as saying in a hadith by Abu Hurairah:
"He who does not desist from obscene language and acting obscenely (during the period of fasting), Allah does not need that he did not eat or drink." (Bukhari Muslim)
In another hadith by Abu Hurairah (RAA), the Prophet (saas) said: "Fasting is not only to restrain from food and drink, but fasting is also to refrain from obscene (acts). If someone verbally abuses you or acts ignorantly towards you, say (to them) 'I am fasting; I am fasting.'" (Ibn Khuzaimah)
Indeed, these two reports imply fasting will not be complete until one observes three elements:
1. Restraining the stomach and the private parts from the breakers of fast - food and drink,
2. restraining the jawarih, the other body parts, which may render the fast worthless despite the main factors of hunger and thirst; so the tongue, for instance, must avoid backbiting, slander, and lies; the eyes should avoid looking into things considered by the Lawgiver as unlawful; the ears must stop from listening to conversations, words, songs, and lyrics that spoil the spirit of fasting; and,
3. restraining the heart and mind from indulging themselves in other things besides dhikir Allah (remembrance of Allah)