The Fourth Pillar of Islam is called The Fast of Ramadan.
Fasting is not exclusive to Islam and is a practice very common in many religions, traditional or not.
The fast occurs once a year, during the 9th lunar month, which is called "the month of Ramadan", the 9th month of the Islamic calendar. During this month, according to the Quran itself:
“…the Quran was sent down as a guidance for the people.” (Quran 2:185)
It is also stated that god exempts ill people, travelers and others who would be in conditions unfit for fasting Ramadan.