Raw physical brawn. This will typically be used for damage dealt in melee combat, feats of strength that check against the physical capabilities of a character, and similar tests of raw muscle. Higher strength should be reflected in character descriptions in terms of size. As a scale:
0: All the physical power and brawn of a particularly limp corpse.
1: Weak adult, child, likely to get sand kicked on them at the beach.
2: Average human adult, can throw a punch and it won't necessarily be like an adorable kitten pawing at a face.
3: Athletic adult, capable of making others feel bad as they demonstrate pushups and chinups.
4: The type of warrior that can provide a demonstrative retort with a warhammer to individuals talking about speed and agility being vastly superior to physical strength.
5: A noble of House Redrain that makes believable claims about wrestling bears, and bears noticeably avoid her in the wild.
6: "...and lo, with a greatsword thrice as long as any man, the demonic lord of hell cleaved the defender in twain."