The foreign exchange market is the marketplace, a point-of-meeting where the, you guessed, foreign currencies are traded and exchanged.
Currencies are essential to both business and individuals from across the globe, whether they acknowledge that or not.
This is all due to a fact that different national currencies (such as Dollar, or Euro, Japanese Yen or Polish Zloty) need to be exchanged in order for the cross-border trade and business relations to exist. So if you are living in America. and want to buy wine from France, then either you personally or the middlemen firm that you buy it from just have to check out with the French producer not in US dollars, but in their (supra) national currency – Euro. Or if you pay these French people with dollars, eventually they will have to convert it to their currency at the end of the day.