Re: So, (from down here in the antipodes)
It means the major ISPs have agreed(*) to provide an option to filter "unsuitable" content (because - see icon). Some weeks I ago I had checked my own account settings I was very surprised to see that the default setting there was opt-out.
As one would expect the definition of "unsuitable" is suitably vague (at least whatever definitions I've seen have left me with more questions than answers).
I must admit that Virgin is my ISP. In my defence may I point out that my router's DNS settings point elsewhere and I appear to have been completely missed by this outage, reading about it on El Reg is the first I've known about it.
(*) for "agreed" read - "bullied by the, pure as driven snow, tabloid press".