Time Zones and Time are really interesting and really confusing. So much so that there isn’t a consistent way that all software/websites implement it. Municipalities around the world decide for themselves what time zone they will adopt and it may change over time. Add in Daylight Savings Time (DST) and it becomes an even bigger mess. Consider that when you “Fall back” the same time on the same date occurs twice—software nightmare :) And there are some countries that have 15 minute time zones. So software really has to consider Time as two things—a universal moment in time and a local perception of time.
Since time zones, in general, are subdivided into one hour slices and municipalities can decide which they adopt and whether they use DST, there are standard databases that software will use that is based on Region like TZ database and IANA. An earlier answer referred to Regions when it identified time zone as Chicago GMT-5, Denver GMT-6, etc.
So really, the short answer to your question is, it depends :)