UTC — Coordinated Universal Time
UTC is the reference every other time zone is defined against. It never observes daylight saving, which is why aviation, computing and international coordination all schedule against it.
UTC vs GMT
UTC and Greenwich Mean Time share the same offset (zero) but are different things. GMT is a time zone used in the UK during winter; UTC is a time standard maintained by atomic clocks and kept within 0.9 seconds of Earth's rotation by leap seconds. In everyday use the difference is negligible; in precise timekeeping it matters.
The "Z" suffix in ISO 8601 timestamps (for example 2026-08-28T22:00:00Z) means UTC — "Zulu" in the NATO alphabet.