What is a UTC offset?
An offset such as UTC+8 says that a local clock is eight hours ahead of UTC at that instant. It does not identify a city, country, daylight-saving policy, or historical rule.
What is an IANA time zone?
An IANA identifier such as Asia/Hong_Kong or America/New_York points to a rule set. Conversion libraries use the date together with that rule set to determine the appropriate offset and abbreviation.
Several zones can share one offset
Asia/Hong_Kong, Asia/Shanghai, and Asia/Singapore commonly display UTC+8 today, yet they remain separate zones because their histories and civil-time authorities differ. A shared current offset does not make their complete rule sets identical.
When should each be used?
Use an explicit offset when recording an already-known instant in an ISO timestamp. Use a named zone for recurring meetings, future schedules, or any conversion that must follow local rule changes. For durable data, many systems store the instant in UTC and keep the named zone separately when local intent matters.