Some Ships, Station Kits, and Drones have damage soaks to certain types of damage. If a ship has energy soak, any energy shots that hit will have their damage reduced by the value of the soak, not a percent. This affects recoil damage too; if an immolation is used on a ship with 5 fire soak, that ship will take 5 less damage per bullet from using it. As such, soaks are an important factor in selecting the right ship.
A negative soak value indicates the ship having a weakness to that type of damage; any weapons of that damage type will do increased damage by that value.
Some diffusers supply additional soaks, as is the case for many high end Dampeners.