A put option which is sometimes simply call as put is a name given to a financial contract between two parties, the seller (writer) and the buyer of the option. a short position has been acquired by the buyer and it is there right, but not obligation, to sell the underlying instrument at an agreed-upon price (the strike price). If the right has been exercised by the buyer that is granted by the option then the seller has the obligation that he has to purchase the underlying at the strike price. For having this option, fees (the option premium) has been paid by the buyer to the writer. The terms for exercise differ and that depends on option style.
The holder is allowed by the European put option that he can exercise the put option for a short period of time right before expiration, while by an American put option the holder is allowed to exercise at any time before expiration.
The put options that are most widely-traded are the put options on equities. However, there are many other instruments on which options are traded such as interest rates or commodities.
