The market value of that home may have doubled to $800,000. But because the down payment locked in a pre-determined price, the buyer pays $400,000. Now, in an alternate scenario, say the zoning approval doesn’t come through until year four. This is one year past the expiration of this option. Now the home buyer must pay the market price because the contract has expired. In either case, the developer keeps the original $20,000 collected.
Many day traders who trade futures, also trade options, either on the same markets or on different markets. Options are similar to futures, in that they are often based upon the same underlying instruments, and have similar contract specifications, but options are traded quite differently. Options are available on futures markets, on stock indexes, and on individual stocks, and can be traded on their own using various strategies, or they can be combined with futures contracts or stocks and used as a form of trade insurance.
Conversely, a put option is a contract that gives the investor the right to sell a certain amount of shares (again, typically 100 per contract) of a certain security or commodity at a specified price over a certain amount of time. Just like call options, a put option allows the trader the right (but not obligation) to sell a security by the contract's expiration date.
Options are available as either a Call or a Put, depending on whether they give the right to buy, or the right to sell. Call options give the holder the right to buy the underlying commodity, and Put options give the right to sell the underlying commodity. The buying or selling right only takes effect when the option is exercised, which can happen on the expiration date (European options), or at any time up until the expiration date (US options).
The price at which you agree to buy the underlying security via the option is called the "strike price," and the fee you pay for buying that option contract is called the "premium." When determining the strike price, you are betting that the asset (typically a stock) will go up or down in price. The price you are paying for that bet is the premium, which is a percentage of the value of that asset.