Definition
A seasonal adjustment of local civil time, in which clocks are advanced one hour from standard time during part of the year (typically spring through autumn) to shift an hour of daylight from the morning to the evening. In the United States it begins on the second Sunday in March and ends on the first Sunday in November. Daylight Saving Time affects local clock time only; it does not affect Coordinated Universal Time (UTC/Zulu), which aviation uses for flight planning, weather products, NOTAMs, and ATC operations.
Plain English
It's the practice of moving local clocks forward one hour in spring and back one hour in autumn, so evenings stay lighter for longer. The time pilots actually fly by — UTC, also called Zulu — does not change.
Context Anchor
Seen in time zone, flight planning, weather briefing, and airport operating-hours discussions.
Derivation
The phrase means 'time that saves daylight' — the idea is that by shifting the clock, more usable daylight falls during waking hours. The concept dates to the early 1900s as an energy-saving measure. Knowing this helps pilots remember that only the local clock label changes; the actual position of the sun and the underlying UTC time do not.
Why Pilots Care
Failing to apply the correct offset can cause errors in departure times, arrival estimates, and coordination with air traffic control.
Intuition Check
Daylight Saving Time does not add daylight and it is not used everywhere. It means the local clock may be one hour different from standard time, so always check whether a listed local time is standard time or daylight time.
Example Sentence 1
Because Daylight Saving Time was in effect, the pilot subtracted four hours instead of five from local Eastern time to get UTC for the flight plan.
Example Sentence 2
A flight plan filed in standard time needs adjustment once Daylight Saving Time takes effect to keep all times consistent.