Nice little video from the BBC:
From the accompanying text (with a somewhat unfortunate headline, as FT noted on twitter last night):
They are the skeletal remains of the victims that have been preserved under a thin veneer of plaster, to give them their life form.
“Until now, these figures have been dispersed around Pompeii itself, or to other museums around the world,” says Grete Stefani, the organiser of the exhibition at the nearby Antiquarium de Boscoreale, a five-minute drive from Pompeii.
“They’ve never been seen together.” [...]
UPDATE (a few hours later): Francesca Tronchin has made a couple of good comments on this, including a link to a very interesting article by Eugene Dwyer, From Fragments to Icons: Stages in the Making and Exhibiting of the Casts of Pompeian Victims, 1863-1888 (just in case you don’t see the comments).