A Contract for Difference refers to a leveraged tradable instrument that mirrors the movements of the underlying asset. It allows for profits or losses to be realized when the underlying asset moves in relation to the position taken; but the actual underlying asset is never owned by the trader. 

Essentially, it is a contract between a client and a broker, who are exchanging the difference in the current value of an equity, currency, commodity or index and its value at the contract's end.