The foreign exchange market (known by the acronym FOREX - for "Foreign Exchange") is a decentralised market where currencies from all over the world are traded. Characterised by a high volume of transactions, deep liquidity and continuous operation (with the exception of weekends), the FOREX market is the world's largest financial market. Historically, FOREX developed in the 1970s with the adoption of floating exchange rates, a system allowing currencies to fluctuate according to supply and demand on the international market (a major transition from the Bretton Woods system of fixed exchange rates introduced after the Second World War). The main players in this market include central banks, financial institutions, multinational companies, institutional investors and individual traders. The market operates mainly via electronic networks or over-the-counter (OTC) transactions, rather than via centralised exchanges. Currencies are quoted on FOREX in the form of currency pairs. The first currency is the base currency and the second is the quote currency. For example, the EUR/USD pair is the exchange rate between the euro (denoted EUR) and the US dollar (denoted USD); the single currency is the base currency and the greenback is the quote currency. Currency pairs are generally classified into three broad groups according to their liquidity levels: major currency pairs, minor currency pairs and exotic currency pairs.