This mean time offset from UTC
This could vary between summer time and winter time:
env TZ=Europe/Paris LANG=C date +"%F %T.%N %z" 2015-12-07 09:28:18.664129444 +0100
Because, we are now using winter time, but
env TZ=Europe/Paris LANG=C date +"%F %T.%N %z" -d '2015-08-01' 2015-08-01 00:00:00.000000000 +0200