The future prices of bitcoin increased 18 percent to more than $18,000 on Monday morning on the Chicago Board Options Exchange. Futures are a type of contract in which a buyer and a seller agree on a price for a particular item to be delivered on a date in the future. Future contracts are available for nearly everything that can be sold such as wheat, soy, gold, oil, cocoa and, now, bitcoin. The demand for bitcoin futures slowed the trading in the Chicago exchange. At times, trading on the site was not available. The price of a bitcoin itself has gone up from $1,000 at the beginning of 2017. As of December 11, it was $16,511 on the bitcoin exchange Coindesk. Bitcoin is different from other national currencies that are supported by governments and national banks. It is not a coin or printed on paper. It is stored as a line of computer code.