When you place spread bets in the forex market, you are betting on currency pair fluctuations. For example, if you believe the euro will rise in value against the US dollar, you can place a spread bet without trading the currency pair.
The spread is the difference between the bid and ask prices quoted by spread betting brokers. Traders then speculate on whether one currency's value will rise or fall in relation to the other. Because the transaction costs less when the spread is low, the currency pair is more appealing.