Fasting Ramadaan as a plillar of Islam

every muslim has the obligation to fast ramaddan, and eat it is a great sin.
Fasting (siyyaam or sawm) is an act of worship which involves abstaining from all food, drink, sexual activity and anything which is bound to break the fast from dawn (the time of calling to the Fajr prayer) utill sunset(the time of calling to the Maghrib prayer).

note: for fasting to be valide, muslims must have the intentions to fast for allah, also the muslim be pure of janabaah and Menstruation and post-natal bleeding for women during the fasting day.

Ramadaan is the ninth month of the Islamic lunar calendar.

also it's one of the best mounth in islam and in muslims tradition, and it contains the gratest night, Laylat-ul-Qadr, the night of qadr, it's the night the quran has came down upon muhamed rusullo allah. the exact date of this night is not known but it came in the last ten days of ramadan, in the days 21, 23, 25, 27 or 29. but muslim scholars had declare the night of 27 to be most likely Laylat-ul-Qadr .

in ramadaan according to rasullo allah who says "When the month of Ramadaan comes, the gates of Paradise are opened, the gates of Hellfire are closed and the devils are chained.(Saheeh Al-Bukhaaree: 3103, Saheeh Muslim: 1079)".

fasting ramadaan  helps realise taqwaa (righteousness, piety, consciousness of Allah, guarding against evil). it provides ample training in refraining from sin and wrongdoing. It helps us remember the needy and the distressed and encourages us to sympathise with them

Paradise has a gate called Ar-Rayyaan through which only those who used to fast will enter, as the Prophet said, in Paradise there is a gate called Ar-Rayyaan, through which only those who fast will enter on the Day of Resurrection, and no one but they will enter it. It will be said, where are those who fasted They will then get up, and none will enter it but them. When they have entered, it will be closed, and no one else will enter. (Saheeh Al-Bukhaaree: 1797; Saheeh Muslim: 1152).

however allah the mercefull has permit his slaves in a certain condition to not fast ramadaan as such :

•   Sick people whose medical condition is bound to be further worsened by fasting are permitted to break the fast but must make up the missed fasts after Ramadaan.
•  People who cannot possibly observe a fast due to old age or sick people for whom there is no hope of recovery may also break the fast but must feed a needy person for every day missed, the amount of food must be given as a recovery for not fasting is determed by the scholars in each society or country.
•  Travellers, while moving from one place to another or during their temporary residence which lasts less than four days, are allowed to break the fast but have to make up for the fast days they have missed after Ramadaan. As the Quran states, "But those of you who are sick or are on a journey must fast an equal number of other days. Allah wants ease for you, not hardship." (Soorat Al-Baqarah: 185).
•  Menstruating women and women experiencing post-natal bleeding are forbidden to fast but must make up an equal number of days after Ramadaan.Even if they fast, it will not be valid.
•  Pregnant and nursing women are permitted to break the fast if they fear it would be dangerous for them or for their babies if they fast. They must, however, make up for the fast days they have missed after Ramadaan.

fasting is a better exercice for our health, so muslim have many days to valunteer fasting such as the first 9 days of the mounf di al-huja especialy the day of arafa, the day of aashuraa, every monday and tuesday of each week, and many more.