Time Zone
timezone
A region of the globe that observes a uniform standard time for legal, commercial, and social purposes.
IANA Time Zone Database
iana tzdb
Overview
The IANA Time Zone Database, commonly known as the tz database or Olson database, is maintained by the Internet Assigned Numbers Authority (IANA). It provides a comprehensive record of UTC offsets, daylight saving transition dates, and historical rule changes for every time zone in the world.
Naming Convention
Time zones are identified using a "Region/City" format, such as Asia/Tokyo, America/New_York, and Europe/London. City names are used rather than country names because many countries span multiple time zones (e.g., the United States, Russia, and Australia). Approximately 600 zone identifiers are defined in the database.
Updates and Usage
The tz database is updated 3 to 10 times per year, with new releases issued whenever a country announces changes to its daylight saving rules or abolishes them entirely. Linux, macOS, Windows, Java, Python, and JavaScript (via the Intl API) all rely on this database for time conversions. Keeping systems up to date is essential for accurate results - running an outdated version can produce incorrect conversions for affected regions.
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