Fasting is primarily an act of willing abstinence or reduction from certain or all food, drink, or both, for a period of time. An absolute fast is normally defined as abstinence from all food and liquid for a defined period, usually a single day (24 hours), or several days. Other fasts may be only partially restrictive, limiting particular foods or substances. The fast may also be intermittent in nature. Fasting practices may preclude sexual intercourse and other activities as well as food.