What is UTC?
Coordinated Universal Time (UTC) is the global reference for civil timekeeping. It is the modern successor to Greenwich Mean Time (GMT) and is the time scale against which every other time zone in the world is defined. When you see a label like "UTC+5:30" or "UTC-8:00", it tells you how far ahead of or behind UTC the local clock is at that moment.
UTC vs GMT
For everyday use, UTC and GMT can be treated as the same thing. They differ by less than a second — UTC is kept in step with the rotation of the Earth by the occasional insertion of a leap second, while GMT is a more loosely defined astronomical time. International standards bodies switched to UTC in 1972; legacy contexts (the United Kingdom's civil time, parts of aviation) still refer to it as GMT. Either way, your laptop's clock and your calendar app are using UTC under the hood.
Why UTC matters for distributed teams
Inside a calendar invite, every meeting is ultimately stored as a UTC instant plus an IANA time zone for display. The display zone tells the calendar how to render the meeting on each attendee's screen; the UTC instant guarantees that both attendees are talking about the same moment in time, even if one of them is on the other side of a daylight-saving transition.
For written communication — emails, chat messages, change requests — the safest convention is to quote times in either UTC or in an unambiguous IANA identifier. "Let's meet at 14:00 UTC" or "Let's meet at 14:00 Europe/Berlin" can be read correctly by anyone in the world. "Let's meet at 14:00" cannot. ZoneShift's individual time zone pages always show you the current local time alongside its UTC equivalent, so you can convert in either direction at a glance.
Half-hour and quarter-hour offsets
Most time zones are an integer number of hours ahead of or behind UTC, but several important ones are not. India is at UTC+5:30, Iran is at UTC+3:30 (or +4:30 in DST), Newfoundland is at UTC-3:30, and Nepal is at the famously precise UTC+5:45. If your team includes someone in one of these zones, never round the offset to a whole hour in your calendar — you will be 15 to 45 minutes off, which is enough to miss the start of a meeting entirely.