What is IP address '::1'?

::1 is the loopback address in IPv6. Think of it as the IPv6 version of 127.0.0.1.

See http://en.wikipedia.org/wiki/Localhost

Just to add little more info to it, in IPv6 loopback address is represented as 127 zeroes followed by a 1 i.e (0000... 127 times..1). It's representation should have been like this -> 0000:0000:0000:0000:0000:0000:0000:0001 but we have some short form representation for this. If there are all zeroes in a single block you can replace it by single 0. So it becomes -> 0:0:0:0:0:0:0:0001. Again we can see that we have runs of zeroes, they can be eliminated and we get -> ::0001 -> ::1 .