Trading session
A trading session is the active period of a major financial centre: Sydney, Tokyo, London or New York. Forex passes from one to the next.
Forex is open continuously during the week, but activity changes with the clock. The Asian session (Tokyo) is often quieter on European pairs. London opens around 8:00 UK time and carries a large share of volume. New York starts around 8:00 a.m. local time, 13:00 in London.
The London–New York overlap, roughly 13:00 to 17:00 UK time, is usually the most liquid part of the day on EUR/USD and GBP/USD: tight spreads, clean moves and plenty of US data.
Watch the clock changes: the US and Europe don't switch to and from daylight saving on the same dates, which shifts session times for a few weeks each year.