Plain English Meaning
Zulu time is the one clock the whole aviation world uses, so everyone is talking about the same moment no matter where they are. It is the time in Greenwich, England, written in 24-hour format with a Z on the end.
Full Definition
Zulu time is the aviation term for Coordinated Universal Time (UTC), the single worldwide time standard used in flight planning, weather reports, NOTAMs, flight plans, and air traffic control communications. It does not change with time zones or daylight saving and is written in 24-hour format followed by the letter Z (for example, 1430Z).
Context Anchor
Seen in METAR time groups, such as 131753Z, where the Z shows the time is in Zulu time, not local time.