It means 'multiple' as in 'A block of flats'. With IPv6 you aren't assigned a single address. You are assigned a contiguous range of addresses. IDNet issues what's called a /48 (I think most ISPs do). What that means in practical terms is that we get assigned a range of addresses that all have the same values in the highest 48 bits. And yes, that does indeed mean that we get assigned a large number of address - 2^80 in fact.
i know with IPv4, you just connected and away you go, but from what i understand, ipv6 isn't as straight forward as that, and wondered why there was a limit to how many IPv6 addresses you could have.Oh it's straightforward for most people. It's only if you need to expose servers to the outside world that things can get complicated. For the average home user it's just as 'plug in and go' as IPv4. Possibly more so thanks to stateless auto-configuration.
Brilliant, thanks for the detailed reply Andrue.