Spread is the different between bid price and offer price, for example the bid price of eur/usd is 1.5520 and the offer price is 1.5522 , then the spread for that pair is 2. Spread usually used by most brokers as their main profit. every broker have different spread each other, and different spread between each currency traded.

Spreads are so important in Forex Trading, as your main role in trading is buying low and selling high. Higher spread means you’re losing more in start than lower spreads. The tighter the spread, the better for you. But tight spreads are meaningful only when they are coupled with good execution.

If you choose to buy the base currency (to long the pair), relying on your expectations of its increase should you buy it on the purchase price which is always higher than the selling price, and you lose the spread difference when you suddenly decide to sell the currency at once. Simply put, the rise of the currency price you bought may cause you the loss.