Strength: (The sheer amount of physical strength one has; to lift heavy objects, move obstacles, or hold back zombies from behind a barricade. Minimum strength thresholds allow certain actions)
Speed: (How fast you can move and react. You should be able to outrun enemies with this. If you are faster than the zombies, you could be very good with a melee weapon, able to do several attacks in a given turn)
Stealth: (How good you are at avoiding awareness checks from zombies or even other humans. This can help you hide from them. However, some creatures can smell you, or sense your heat source...)
Awareness: (How good you are at noticing hidden objects, or detecting clues, or sensing other players. High awareness allows you to gain a better sense of your surroundings and notice dangers.)
Combat: (How good you are at fighting, in terms of training and accuracy and deflecting blows. The better this rating is, the better you will survive assaults by trained forces or zombies. But nothing stops a bullet to your head or an explosive to your gut)
Luck: (This is your saving throw in case your other skills aren't up to snuff. It can help you avoid bullet fire and also help you "accidentally" make correct decisions, if you decide to flee from danger, your luck might make you flee in the correct direction.
Vitality: How much damage you can take before dying