There are 25 integer World Time Zones from -12 through 0 (GMT) to +12. Each one is 15° of Longitude as measured East and West from the Prime Meridian of the World at Greenwich, England. Some countries have adopted non-standard time zones, usually 30 minutes offset which have a * designation. 

Each Time Zone is measured relative to Greenwich, England. There are both civilian designations which are typically three letter abbreviations (e.g. EST) for most time zones. In addition there are military designations. These use each letter of the alphabet (except 'J') and are known by their phonetic equivalent. E.G. Greenwich Mean Time (civilian) or Z = Zulu (military and aviation). 

TZ-Olson 

TZ-ISO-3166-1