What does ray splitting mean?

The 4-, 8- and 16-ray description refers to the number of terminal branches of each individual ray. If the caudal (tail) rays divide (split, branch), then divide again, you’ve got 4-ray splitting (1rayx2×2=4): if they divide 3 times, 8 rays (1×2x2×2): 4 times, 16 rays (1×2x2×2x2) and so on.

Thanks to Vicky for this description!