U10 and other such numbers are references to size. So U10 means that there are under 10 squids in a kilogram. The lower the number, the bigger the squid.
Shatterpacks contain fish or seafood that is packed and separated with a polythene sheet. The shatterpack prevents the seafood from sticking together. The shatterpack can be struck or dropped against a hard surface to break apart individual cuts or pieces of seafood.