Physical power. Affects carrying capability and damage with many melee and thrown weapons. Affects throwing range.
Perception
Senses and intuition. Affects chance to detect hard-to-notice people/places/things. Affects accuracy with ranged weapons.
Endurance
Hardiness and resilience. Affects health, healing rate, and similar things.
Force of personality. Affects speech skills and other character interactions.
Intelligence
Reasoning ability. Affects academic skills.
Agility
Balance, speed, and grace. Affects combat speed and efficiency as well as several skills.