You are weakly built and have less pure muscle power than others. Use this trait whenever raw strength is in question. This trait reduces your encumbrance limit by 1kg per step of the trait. If you have -2, your encumbrance limit is 10 kg instead of 12 kg. It also means you have a rather lean frame. While weapons are an excellent force multiplier, your weak build means you can't swing them as effectively and the trait is a penalty on all your melee attacks. It only applies to the Lethality of your attacks, not your ability to hit. So apply the penalty after counting Excess.
Cannot be taken if your character also has Strong.