Some creatures have been given a value of '0' (often shown as a dash: '-') for certain characteristics, which means that they have no ability whatsoever in that skill. This usually applies to creatures unable to use missile weapons, so they have BS0 or BS-, but it might equally well apply to other characteristics too. For example, some creatures or war machines may have no Attacks (A0 or A-).
If any creature or object has a Weapon Skill of 0 then it is unable to defend itself in close combat, and any blows struck against it will therefore automatically hit.
If at any time a model's Strength, Toughness or Wounds are reduced to 0 or less by magic or a special rule, it is slain and removed from play.