What does "::" mean?

[could ildg]

I know that ":" can do slice works.
But I saw "::" today and it puzzled me much,
I can't find it in the python doc,
so I raise this question here.
The code is as below:
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Jython 2.2a1 on java1.5.0_03 (JIT: null)
Type "copyright", "credits" or "license" for more information.
>>> live='live';print live
live
>>> live=live[::-1];print live
evil
>>>
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"[::-1]" can reverse a string magicly, how did it do it?