Question

From /usr/share/postgresql/timezonesets/Default:

#################### AUSTRALIA ####################

ACSST   37800 D  # Central Australia (not in zic)
AESST   39600 D  # Australia Eastern Summer Standard Time (not in zic)
AEST    36000    # Australia Eastern Standard Time (not in zic)
AWSST   32400 D  # Australia Western Summer Standard Time (not in zic)
AWST    28800    # Australia Western Standard Time (not in zic)
CADT    37800 D  # Central Australia Daylight-Saving Time (not in zic)
CAST    34200    # Central Australia Standard Time (not in zic)
LHDT    39600 D  # Lord Howe Daylight Time, Australia (not in zic)
LHST    37800    # Lord Howe Standard Time (Australia)
                 #     (Australia/Lord_Howe)
LIGT    36000    # Melbourne, Australia (not in zic)
NZT     43200    # New Zealand Time (not in zic)
SADT    37800 D  # South Australian Daylight-Saving Time (not in zic)
SAST    34200    # South Australian Standard Time (not in zic)
WADT    28800 D  # West Australian Daylight-Saving Time (not in zic)
WAST    25200    # West Australian Standard Time (not in zic)
WDT     32400 D  # West Australian Daylight-Saving Time (not in zic)

So there are some daylight-saving time entries in there, but for “Eastern” it says instead “Eastern Summer Standard Time”. What is that?

Answer 1

“Summer Standard” is an older name for “Daylight-Saving”. See the Australian Government Time page for official definitions.