Coordinated Universal Time or UTC (from the French, temps universel coordonné), is the standard by which the world regulates clocks and time. When expressing a time independent of any one time zone, UTC is the standard. It does not use Daylight Savings Time.
Since Waze is a worldwide platform with editors from every time zone, it is sometimes confusing to coordinate map activities or check when an edit was made. Waze stores many time values in UTC format and converts for local usage. For example, turn restrictions are input and evaluated (for routing) in local time for the location of the segments, but may be stored in UTC.
For coordination activities (especially MapRaids), to avoid confusion, it is preferred to express times in UTC, or UTC and additional local time zones for the editors and map area.
Other time zones have their time expressed as an offset from UTC. For example, the Eastern Standard Time zone (EST - east coast of the US and Canada) is UTC-5, or 5 hours slower than UTC. During the summer, EST observes Daylight Saving Time, and becomes UTC-4.
Greenwich Mean Time, or GMT, was used before UTC replaced it. They are usually the same time.
The Time and Date web site has tools to easily convert time zones.