tz

tz commonly refers to the IANA Time Zone Database, also known as tzdata or the Olson database. It is a collaborative, public-domain collection that records the historical and current time zone rules for most regions of the world. The database enables accurate conversion between local time and Coordinated Universal Time (UTC) and is used by a wide range of software, operating systems, and programming languages.

The database organizes data by region-based zone names such as Africa/Cairo, America/New_York, and Europe/London. Each zone defines the standard time offset from UTC and the daylight saving time rules that apply to different periods. The data is structured with Zone records, Rule sets that describe when DST starts and ends, and Link entries that provide aliases for zones. tzdata is distributed as plain text files and, in practice, is compiled into a binary zoneinfo database used by software to perform time calculations.

Maintenance and usage: tzdata is maintained by the Internet Assigned Numbers Authority (IANA) with contributions from volunteers, including long-time maintainer Paul Eggert. Updates are issued to reflect changes in DST rules or political decisions affecting time zones. Most Unix-like systems ship with tzdata and receive updates through their package managers; many programming environments (such as Python, Java, and Ruby) incorporate the data to handle time zone conversions correctly.

Impact and limitations: While comprehensive, the database relies on timely updates and ongoing governance. Historical zones can be complex, and some regions may have incomplete historical records. Nevertheless, tz remains the de facto standard for time zone information in computing.