Options are derivative instruments, meaning that their prices are derived from the price of their underlying security, which could be almost anything: stocks, bonds, currencies, indexes, commodities, etc. Many options are created in a standardized form and traded on an options exchange like the Chicago Board Options Exchange (CBOE), although it is possible for the two parties to an options contract to agree to create options with completely customized terms.
There are two types of options: call options and put options. A buyer of a call option has the right to buy the underlying asset for a certain price. The buyer of a put option has the right to sell the underlying asset for a certain price.
Here's a brief look at a few of the most common types of options:
Every option represents a contract between the options writer and the options buyer.
The options writer is the party that "writes," or creates, the options contract, and then sells it. If the investor who buys the contract chooses to exercise the option, the writer is obligated to fulfill the transaction by buying or selling the underlying asset, depending on the type of option he wrote. If the buyer chooses to not exercise the option, the writer does nothing and gets to keep the premium (the price the option was originally sold for).
The options buyer has a lot of power in this relationship. He chooses whether or not they will complete the transaction. When the option expires, if the buyer doesn't want to exercise the option, he doesn't have to. The buyer has purchased the option to carry out a certain transaction in the future -- hence the name.