Based on the code snippet it seems that CT images are loaded (hu_a should refer to Hounsfield units).
origin_xyz would refer to the origin of the Cartesian coordinate system, vxSize_xyz to the voxel size in each direction, and direction_a should be an axis vector.
The asterisk (*) unpacks the values as described e.g. here 4.
CC @tom, who is one of the authors of this book to correct me.