Understanding UTC and GMT

UTC (Coordinated Universal Time) is the civil time scale timezones are defined against. GMT historically meant mean solar time at Greenwich. In everyday use people still say GMT for UK winter time, but software should store IANA identifiers such as Europe/London rather than a fixed GMT offset.

A UTC offset such as UTC+01:00 is the difference at a specific instant. It can change when daylight saving starts or ends. This site never treats a stored offset as the primary timezone.