In this paper, on page 10, the authors describe the group of motions of "galilean space" as $IISO(1)$. I can't find any definition of this group within the paper, or online.
It's used alongside $ISO(2)$ for the group of motions of $2d$ Euclidean space. They also use $ISO(1,1)$, which I think is defined on page 261 here.
What group does $IISO(1)$ refer to?