CFD stands for contract for difference. This means it is an agreement between you and your broker to exchange the difference between the opening price and closing price of a contract. Hence, you speculate on the movement of the underlying asset (a stock, commodity, etc.), but you do not own the asset.
One of the most unique aspects of CFDs is that they enable you to profit from falling markets as well as rising ones. For more details you can check our video on the CFDs here.