It is an acronym for single stock futures option, which is an American-style option in which the underlying is a single stock futures (SSF) or individual equity futures. This option is exercisable into the underlying futures contract (SSF) and consequently into the underlying of the futures contract itself. In other words, upon expiration of an SSF option, the buyer and seller of the option become then the buyer and seller of a single stock futures. Typically, an SSF contract is physically settled, i.e., the buyer (the long position holder) of the futures contract takes delivery of the actual underlying from the seller (the short position holder).