The forex market is able to stay open 24 hours a day five days a week because forex trades over the counter . It does not trade at one central location. Forex trading is carried out using electronic communication networks in different locations around the world, mostly by big banks, and for a variety of different players.
Source: Bank of International Settlements Triennial Report from 2016, prepared by Warren Venketasand during the overlap. The overlap is a four-hour period of time from 8AM ET to 12PM ET when the New York session and the London session overlap leading to increased liquidity and volatility in the market.