This is a special address for the loopback interface, similiar to IPv4 with its ”127.0.0.1”. With IPv6, the localhost address is:
0000:0000:0000:0000:0000:0000:0000:0001
or compressed:
::1
Packets with this address as source or destination should never leave the sending host.
This is a special address like ”any” or ”0.0.0.0” in IPv4 . For IPv6 it's:
0000:0000:0000:0000:0000:0000:0000:0000
or:
::
These addresses are mostly used/seen in socket binding (to any IPv6 address) or routing tables.
Note: the unspecified address cannot be used as destination address.
There are two addresses which contain an IPv4 address.
IPv4-only IPv6-compatible addresses are sometimes used/shown for sockets created by an IPv6-enabled daemon, but only binding to an IPv4 address.
These addresses are defined with a special prefix of length 96 (a.b.c.d is the IPv4 address):
0:0:0:0:0:ffff:a.b.c.d/96
or in compressed format
::ffff:a.b.c.d/96
For example, the IPv4 address 1.2.3.4 looks like this:
::ffff:1.2.3.4
IPv4-compatible IPv6 addresses are used for automatic tunneling (RFC 2893 / Transition Mechanisms for IPv6 Hosts and Routers), which is being replaced by 6to4 tunneling.
0:0:0:0:0:0:a.b.c.d/96
or in compressed format
::a.b.c.d/96