UTC is Universal Time Coordinated. It is not a time zone, and is not adjusted for daylight saving time.

It might help to think about it as a clock placed at 0° longitude.
It is within about 1 second of mean solar time at 0° longitude.

Time zones are positive or negative offsets from the UTC clock.
If you see +05 ending a UTC timestamp, your approximated location is 5 hours later than UTC.

UTC is a compromise between the French TUC (temps universel coordonné) and English CUT (coordinated universal time).

The speed of the Earth's rotation is irregular so leap seconds are occasionally added or removed.