More specifically, the spot market is where currencies are bought and sold according to the current price. That price, determined by supply and demand, is a reflection of many things, including current interest rates, economic performance, sentiment towards ongoing political situations (both locally and internationally), as well as the perception of the future performance of one currency against another. When a deal is finalized, this is known as a "spot deal." It is a bilateral transaction by which one party delivers an agreed-upon currency amount to the counter party and receives a specified amount of another currency at the agreed-upon exchange rate value. After a position is closed, the settlement is in cash. Although the spot market is commonly known as one that deals with transactions in the present (rather than the future), these trades actually take two days for settlement.
One pound on Monday can bring you 1.19 euros. On Tuesday 1.20 euros. This tiny change may not seem like a big deal. But think about it on a larger scale. A large international company may have to pay foreign employees. Imagine what this can do for a practical purpose, if, as in the example above, a simple exchange of one currency for another costs you more, depending on when you do it? These few kopecks add up quickly. In both cases, you, as a traveler or business owner, can keep your money until the forex course becomes more favorable.
Since the market is made by each of the participating banks providing offers and bids for a particular currency, the market pricing mechanism is based on supply and demand. Because there are such large trade flows within the system, it is difficult for rogue traders to influence the price of a currency. This system helps create transparency in the market for investors with access to interbank dealing.