Literally: To abstain in general, for Allah (G. B. H) says:

{T have vowed a fast to (God) Most Gracious, and this day will I enter into no talk with any human being. } [Maryam: 26]

Legally: To abstain from that which breaks one's fast, beginning with a specific intention, throughout a day (From dawn to sunset.

However, one should extend his fast a short time beyond sunset in order to make sure that the day is complete.

Also, scholars of jurisprudence said that it is necessary to abstain from food, and other things that invalidate fasting, a short time before dawn according to the rule that says: Anything necessary to fulfil! an obligation is obligatory) in which fasting is permissible (Because there are some days in which fasting is forbidden as will be explained later).