There's a wikipedia article on naval sheering. Essentially, it's having the bow and stern of a ship slope up toward the ends, so that the ship's movement is more stable, and the forward movement can help with staying afloat. It's really useful in FTD, because battle damage can sink a non sheered bow, while a sheered bow can stay afloat just by acting like a massive hydrofoil.

its what happens when 2000mm cram hits the front of a ship?