The time zone in New York is Eastern Daylight Time (EDT) in the summer and Eastern Standard Time (EST) in the winter. New York uses two time zones depending on the year, because daylight saving time must be accounted for when it shifts time zones worldwide.
A time zone is a geographical area that follows a uniform standard time. There are 24 or 25 time zones in the world, depending on whether the International Date Line is taken into account. Time zones are designed to match internal and international borders of countries, which is why they are not straight. Some large countries use a single time zone, such as India and China. Others use multiple time zones; for example, the United States and Russia.
When worldwide travel and communication exploded, a need for a cohesive and convenient time standard developed, which is why time zones exist.