A futures contract is a set agreement between a buyer and seller for contract to be exchanged in cash for a specific amount of the underlying product (commodity, stock, currency, etc).
Today is the September futures expiration date for Bitcoin Futures. This means that if you bought a September futures contract earlier in the month today would be the day of redemption.
You do have the option to roll over to the next month but this normally costs a fee depending on the broker. Futures contracts are normally divided into a few expiry dates throughout the year. Each of the futures contracts can be traded for a specific amount of time. Then when the contract expires it cannot be traded anymore. The date upon which a futures contract expires is known as its expiration date.
This Bitcoin futures contract settles at 3:00pm CST. The contract size is for 5 bitcoins and if the owners are not happy with the price on expiry technically they can rollover to the next month.
Looking at the futures contract today you can see that the sentiment is still low. The market is still recovering from the fall three sessions ago. The 8,224.0 level is an important resistance and a break could indicate we might get some sort of recovery.