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Author and Publisher, The TCP/IP Guide
Just as certain IPv4 address ranges are designated for reserved, private and other “unusual” addresses, a small part of the monstrous IPv6 address space has been set aside for special addresses. The purpose of these addresses and address blocks is to provide addresses for special requirements and private use in IPv6 networks. The nice thing about IPv6, of course, is that even relatively small pieces of it are still enormous, so setting aside 0.1% of the address space for a particular use still generally yields more addresses than anyone will ever need.
There are four basic types of "special" IPv6 addresses: reserved, private, loopback and unspecified.
A portion of the address space is set aside as reserved for various uses by the IETF, both present and future. Unlike IPv4, which has many small reserved blocks in various locations in the address space, in IPv6 the reserved block is at the “top” of the address space: the ones starting with “0000 0000” (or 00 for the first hexadecimal octet). This represents 1/256th of the total address space. Some of the special addresses below come from this block. IPv4 address embedding is also done within this reserved address area.
Note: Note that reserved addresses are not the same as unassigned addresses. The latter term just refers to blocks whose use has not yet been determined.