Short answer
NO, there is no difference between time zones UTC and Etc/UTC.
Long answer with context
Etc/UTC is a timezone in the Olson-timezone-database (tz database), also known as IANA-timezones-database, in which all timezones conform to a uniform naming convention: Area/Location.
While most timezones (e.g. “Berlin”) can be attributed to an area (e.g. “Europe”, resulting in “Europe/Berlin”), some timezones cannot be attributed to any Area of the world (think continents or oceans). Thus, the special Area Etc (Etcetera) was introduced. Area Etc applies mainly to administrative timezones such as UTC.
In summary: To conform with the naming convention, the universal coordinated time(zone) is named Etc/UTC in the tz database.
Note on tz database and POSIX timezones
For administrative timezones other than UTC (e.g. GMT+4, GMT-8), the tz database uses POSIX-style signs in the zone-names. POSIX has positive signs for zones that are behind Greenwich (west of Greenwich) and negative signs for zones that are ahead of Greenwich (east of Greenwich).
This POSIX convention is the opposite of the definition for timezones in the nowadays widespread and mostly used ISO 8601. In the ISO 8601 timezone format, negative signs indicate that a zone is behind UTC (west of Greenwich) and positive signs indicate a zone is ahead of UTC (east of Greenwich). Examples: “+03:00” in ISO 8601 equals GMT-3 in POSIX; “−05” in ISO 8601 equals “GMT5” in POSIX.
The ISO 8601 convention has become the effective standard nowadays, making POSIX timezones look confusing to some readers.
Possible reasons for POSIX timezone definition
- POSIX is part of UNIX, which was developed in the USA, which is behind UTC (west of Greenwich). The POSIX format allows the US timezones to be represented as EST5 (i.e. “Eastern Standard Time, 5 hours behind Greenwich), PST8 (i.e. “Pacific Standard Time, 5 hours behind Greenwich), i.e. omitting the (+) sign.
- Nowadays, most computer programs and operating systems internally do everything in UTC time. With POSIX-style signs you can add time and timezone in order to get UTC time. Example: “03:30 PST8” or “03:30 GMT+8” means it is “11:30 UTC”.