There are Eight types of Fast. They are as follows:
1. Fardh Mu-'Ayyan: Fasting for the whole month of Ramadan once a year.
2. Fardh Ghair Mu-'Ayyan: The duty upon one to keep Qadha of a fast missed in the month of Ramadan with or without a valid reason.
3. Wajib Mu-'Ayaan: To vow to keep a fast one a specific day or date for the pleasure of Allah I, upon the fulfilment of some wish or desire.
4. Wajib Ghair Mu-'Ayaan: To vow or pledge to keep a fast without fixing any day or date, upon the fulfilment of a wish. Those fasts which are kept for breaking one's Qasm (oath) also fall under this catergory.
5. Sunnah: Those fasts which Rasulullah (saw) kept and encouraged others to keep, e.g., fasting on the 9th and 10th of Muharram, and the 9th of Dhil Hijjah, etc.
6. Mustahab: All fasts besides Fardh, Wajid and Sunnah are Mustahab, e.g., fasting on Mondays and Thursdays.
7. Makruh: Fasting ONLY on the 9th or 10th of Muharram of Fasting ONLY on Saturdays.
8. Haram: It is Haram to fast on FIVE days during the year. They are Eidul Fitr, Eidul Adhaa and three days after Eidul Adha.