For me it is:

Save value: hardness of the first layer of armor of a unit

Toughness: Amount/Mass of non-critical part of the unit that can be damaged without impacting the unit much

Wounds: Amount of critical parts/vital organs of a unit that can be damaged while the unit still lives/operates

Armour Penetration: Ability to break this initial layer of armor (sharpness of the blade or pointiness of the bullet)

Strength: Ability to penetrate/spread through general mass of the shot unit (overall energy of the shot/blow)

Damage: Potential of damaging critical parts/vital organs of a unit (shape of the blade/bullet)

Examples:

Hollowpoint bullet and Armor Piercing bullet could have the same energy (mass x speed) but Hollowpoint has lower AP but higher Damage while Armor Piercing has lower damage but higher AP

A Rabbit and a Bear would have similar Save Value (skin covered only by fur) but Bear would have much greater toughness (a bullet must travel through more bear body to reach organs) and possibly more wounds since a one bullet could damage multiple critical organs of a rabbit but less likely bear