The act of 'rebalancing' the statistics of ships (as a typical example) so that the impact of their performance, real or perceived, in the game is levelled out. Example: the Dooms Day Device, the primary weapon that can only be used by titan-class hulls, has been 'nerfed'. This used to be an area-of-effect type weapon that would instantly obliterate almost all other ships currently on the grid, which made them incredibly powerful weapons. The nerf consists of turning the DDD into a single-shot beam weapon that will completely destroy the ship it's shooting at (keeping in mind that it won't be able to target very small and agile ships).