1. If VIRGO is an acronym, what does it stand for?
The name of the Virgo Collaboration is not an acronym,
and it is commonly written in non-all-caps form, as
I just did.
It is named after the Virgo cluster of galaxies, of which
the local group is a member. The cluster is in turn named
for the constellation Virgo, since the center of the cluster
is in that part of our sky.
The name is significant, since the current generation of
instruments was designed to detect the coalescence of a
compact binary star system anywhere within the Virgo cluster.
You have to look at a volume of that magnitude if you want
to see coalescence events at a reasonable rate.