A Timezone is unambiguously defined by the set
of time measurement rules determined by the governing body for a given
geographic area. These rules describe at a minimum the base offset from UTC
for the time zone, often referred to as the Standard Time offset.
Many locations adjust their Standard Time forward or backward by one hour, in order to
accommodate seasonal changes in number of daylight hours, often referred to
as Daylight Saving Time. Some locations adjust their time by a
fraction of an hour. Standard Time is also known as Winter Time. Daylight Saving
Time is also known as Advanced Time, Summer Time, or
Legal Time in certain countries. The following
table shows the changes in time zone rules in effect for New York City
starting from 1967. Each line represents a description or rule for a
particular observance.