What does that +0100 value mean in NSDate?

When I look at an NSDate value in the debugger, I get something like this:

1.4.2010 22:01:47 +0100

I don't get it what this +0100 is good for. Sometimes it is +0200. Is that supposed to be the time zone or something like开发者_如何学Go that? What's it exactly? How does it affect the "since reference date" value?

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Timezone.

+0100 means 1 hour ahead of UTC (GMT).