Arabic (فاسد) for unsound, invalid, voidable, not viable, foul, or corrupt. It is usually used to describe an act or aqd (contract)  that involves or includes an impermissible term or condition rendering it invalid. For example, the sale of dates to be delivered when ripened is a fasid transaction as it is embedded with an invalid stipulation. Fasid contracts can be, and must be, annulled unilaterally, i.e., without the consent of either party.