Similarly, if you believe the company’s share price is going to dip to $80, you’d buy a put option (giving you the right to sell shares) with a strike price above $80 (ideally a strike price no lower than $80 plus the cost of the option, so that the option remains profitable at $80). If the stock drops below the strike price, your option is in the money.

With respect to an option, this cost is known as the premium. It is the price of the option contract. In our home example, the deposit might be $20,000 that the buyer pays the developer. Let’s say two years have passed, and now the developments are built and zoning has been approved. The home buyer exercises the option and buys the home for $400,000 because that is the contract purchased.
An option is a contract that allows (but doesn't require) an investor to buy or sell an underlying instrument like a security, ETF or even index at a predetermined price over a certain period of time. Buying and selling options is done on the options market, which trades contracts based on securities. Buying an option that allows you to buy shares at a later time is called a "call option," whereas buying an option that allows you to sell shares at a later time is called a "put option." 
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