A number of pages in the Wiki that are about handling time values refer to GMT. I think it’s true to say that a global search-and-replace should be used to change those references to “UTC”.
Here in the UK, on the 26th October, we had the annual switchover from BST (British Summer Time, UTC+1) to GMT (Greenwich Mean Time, UTC+0). GMT will be in use until 29th March, at which point it will again be put up in the attic and not be in use. UTC is of course constant throughout the year. Nowadays, the venerable GMT can be seen as one of several local names that are regarded as equivalent to the universal (well, global 
) UTC+0.
Wikipedia says (providing sources):
English speakers often use GMT as a synonym for UTC.[8] For navigation, it is considered equivalent to UT1 (the modern form of mean solar time at 0° longitude); but this meaning can differ from UTC by up to 0.9 s.[e] The term "GMT" should thus not be used for purposes that require precision.[9]
The Unix Epoch was defined in terms of Coordinated Universal Time (UTC).
I look forward to any disagreements or observations on the subject!