A four-legged creature with no arms.
This Metatrait is defined on page 263 of the Basic Set.
In Plain Terms:
A Quadruped (by definition) has four legs, giving him the 5 point version of "Extra Legs". This lets them move at full Move even if they lose a leg, with only the loss of two causing them to fall down and gives them two extra limbs to use in play which they cannnot use it to manipulate.
Quadrupeds also have a Horizontal Posture, allowing them to at best stand on their hind legs for short periods (which is very uncomfortable). They can use one "hand" while standing on your other limbs, or two "hands" while sitting on your haunches, with Move 0 in either case. Quadrupeds cannot their full weight behind a kick, suffering a -1 damage per die when you kick, unless they have the Claws (but not Hooves) advantage.
Finally, a Quadruped has the "No Fine Manipulators" disadvantage, meaning he has no limb that can manipulate objects better than a paw/hooves. You cannot use your limbs to make repairs, pick locks, tie knots, wield weapons, etc., or even to grasp firmly.
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