The time zone difference between the local time zone and UTC.
The number of seconds between the local time zone and the UTC time zone.
The "TimeZoneBias" returns an integer representing the number of seconds you would need to add to the local time in order to put it into the UTC time zone. This number will be positive if UTC is ahead and negative if it is behind. If you want to adjust a given time, it's more convenient to use the FromUTC or ToUTC services. This service is here in case you are interested in the actual bias value.
Note: This service takes daylight savings time into account.