SLAAC is basically an IPv6 alternative to how DHCP works. With IPv6, you can either use DHCPv6 (ISPs deliver Prefix Delegations and Normal Addresses this way) or SLAAC (How one typically gets an IPv6 address on a LAN or route from a Link-Local address on an ISP).

Hopefully that's clear as mud ;) I would encourage you to go check out IPv6 if that was the intent of your original question. It actually makes more sense after you dive in, and can be pretty neat.

ULAs (Unique Local Address) are one often-overlooked part of which I'm an advocate.