TZ definition operating system
The Unix environment variable
containing the current time zone
identifier, e.g. "GMT", "EST".
In early versions of Unix this variable simply contained the standard identifier for the zone, an offset in hours from GMT and an identifier to use during daylight saving time (e.g. "GMT0BST"). In later systems it stores the name of a file containing the details of a particular zone such as the dates when DST is in force. Unix manual page