Fasting is divided into two kinds: Fard, the obligatory fast, and voluntary (Tatawwu'u). any non-obligatory fast. The obligatory fast is categorized into three kinds:
(1) fasting the month of Ramadan
(2) fasting to expiate for religious offenses
(3) fasting to fulfill a vow
Of the three, fasting during the month of Ramadan is the most important; so we will devote most of the discussion to it.
In Islam, deeds do not end with nor rest only on obligatory deeds. Fard are the minimum duties required of an average believer. Thus, the Lawgiver instituted voluntary deeds, to assist a devoted believer who has the will to do more, and also assist the believers in general in repairing and complementing their obligatory deeds with voluntary deeds. The voluntary deed comes with every pillar in Islam, including fasting.
The voluntary fast is for men as well as for women. The method and restriction of this fast is no different from regular Ramadan fast. The difference is in the niyyah (intention).