Champion statistic

A champion statistic is a number indicating how well a champion can do a certain thing. These help define the assets of a champion. There are 18 official statistics, divided into three categories: Offensive, Defensive, and Magical.

Offensive

 * Armor penetration: How much the armor values of targets are reduced during physical damage calculations.
 * Attack damage: Provides the initial damage value of basic attacks and scaling on some abilities.
 * Attack speed: The rate at which a champion uses their basic attack.
 * Critical strike chance: The percent chance that a basic attack will critically strike to deal increased damage.
 * Critical strike damage: The percentage damage increase provided by critical strikes.
 * Life steal: The percentage of the damage done by a champion's basic attacks that is returned to them as health.
 * Movement speed: The speed at which a champion moves around the map.

Defensive

 * Armor: Used to calculate the reduced damage taken from basic attacks and abilities that deal physical damage.
 * Health: The total damage a champion may take before dying.
 * Health regeneration: The rate at which a champion's health is naturally restored.
 * Magic resistance: Used to calculate the reduced damage taken from from abilities that deal magic damage.
 * Tenacity: The percent reduction in the duration that a champion is effected by some crowd control effects.

Magical

 * Ability power: Provides scaling on some abilities.
 * Cooldown reduction: The percent reduction in the time after an ability is used by a champion before it can be used again.
 * Magic penetration: How much the magic resistance values of targets are reduced during magic damage calculations.
 * Mana: The maximum mana available to a champion for casting abilities.
 * Mana regeneration: The rate at which a champion's mana is naturally restored.
 * Spell vamp: The percentage of the damage done by a champion's abilities that is returned to them as health.

Increasing Statistics
All champions begin the game with a certain amount of attack damage, attack speed, armor, health, health regeneration, mana, and mana regeneration. This is commonly referred to as the base value of that statistic for that champion. All champions naturally increase these stats by a certain amount every time they gain a level. Each champion's base statistics and per-level statistics are unique and play a large role in game balance for that champion.

Two statistics that deviate from this pattern are movement speed and magic resistance. Every champion has a unique base movement speed that does not increase naturally, and every champion begins the game with exactly 30 magic resistance. Magic resistance is the only statistic that increases for some champions and not for others. In general, if a champion is ranged or has a ranged form or is classified as a tank, they will not gain magic resistance per level.

All other statistics have a natural value of zero and must be increased by other sources. The ways a champion may increase their statistics are varied and include runes, masteries, items, and auras. Some champion abilities increase that champion's statistics, either as a passive effect ( passively increases Fiora's attack damage) or as an active effect ( briefly increases Ryze's movement speed and spell vamp) or as a effect that follows another action (if uses  on an enemy, he briefly gains attack speed, but he does not get the increase by simply activating the ability).