A CFD (Contract for Difference) is a derivative of a financial product and is used for trading. The CFD price behaves exactly like the underlying asset price.
There is no actual ownership of the underlying asset of reference. A CFD is therefore a derivative product where Saxo Bank is a counterparty to the trade. Since the product is not exchange-traded, it is said to be traded over-the-counter (OTC).
CFDs are traded on margin and can be sold short, making it possible to profit in falling markets or to hedge your stock positions.
You can read more about CFDs here.