What does "high-grade" mean in regards to the Terrapin's shields?

The Terrapin's shields are oversized; it's a small ship, but it carries the kind of shield generator you'd expect on a much larger class of ship, like a Freelancer or Constellation, for example. Of course, an oversized shield generator has oversized power requirements and signature, which is one of the reasons why the Terrapin is also so heavily armored for all the operational reasons indicated above. Ideally, you don't allow yourself to get caught by the enemy in a Terrapin, but when the jig is up and you're spotted, your thick shell will buy you time you wouldn't have in a lighter ship.