An item is an artifact or object carried by champions to enhance their performance on the Fields of Justice. A champion can only carry six items and a Trinket at a time, making the selection of items an important part of achieving victory. Items are only obtainable through the item shop located at the Spawn Pool. This is also where items are sold back for 70% of the total gold spent to obtain them. The exceptions to this are the Prospector, Doran, Gold Income items, Consumables, and Guardian Angel, which return 40% of their total cost.
Items are divided into six categories: basic, advanced, legendary, mythical, consumable, and trinket. A basic item does not require any other items to be purchased. If an item requires the purchase of at least one specific basic item before it can be purchased, that item is considered an advanced item. All basic items required for the purchase of advanced items are consumed when the advanced item is purchased. The same is true for legendary items, which require the consumption of at least one advanced item, and mythical items, which require the consumption of at least one legendary item.
Consumable items are different from other item types in two ways. First, most consumable items may be stacked, allowing duplicates items to occupy the same item slot up to a cap. Secondly, consumable items may be expended to perform a specific function, permanently removing that item from the champion's inventory. On charge-based items such as the Crystalline Flask, the charge is consumable but the item cannot be stacked or consumed.
Every item in the game provides some sort of effect. An item's primary effect is usually statistics, however, many items also possess secondary effects which provide champions with additional benefits beyond raw statistics. Consumables are one exception, as almost all consumables provide no benefits until consumed. In addition, some effects are labelled unique (which is explained below).
Actives are triggered by clicking on the item or by pressing the item's hotkey, and function similarly to a champion ability. These effects have cooldowns before they can be used. The cooldown of activated abilities is not affected by cooldown reduction.
Passives are effects that function automatically, like the passive or innate abilities of a champion.
Auras are buffs or debuffs that affect nearby friendly or enemy units, respectively. All aura effects are unique.
The holder of an aura item is not considered to be under the effects of the aura, and thus can still benefit from an aura. This allows auras to stack up to twice on champions who posses the aura themselves. Other allies will not benefit beyond the first aura.
Consumable items generally provide no benefit until consumed, functioning as an activated item effect. Consumable items are primarily focused on either gaining map control through the use of wards or boosting a champion's statistics for a brief period with potions and elixirs. Consuming an item will either destroy it or consume a charge, similar to stock abilities. Charge-based consumable items are refreshed when the holder returns to their spawning pool.
Some item effects are unique. Typically, a unique effect means that if a champion were to purchase two identical items, the unique effects would only be granted once. Some items grant basic statistics, such as cooldown reduction and spell vamp, with a unique tag to prevent abusive cases where the item could be stacked to exploit the statistics it provides.
Some items feature unique named effects, such as Maim. A named effect is similar to a unique effect, except that the conditions of being unique are global. The effects of the named effect can only be gained once, even if the two items are entirely unrelated (such as Tenacity).
Unless the effect is named, two different items with the same passive will stack. For example, the 10% cooldown reduction from The Brutalizer and Fiendish Codex will stack, however owning multiple The Brutalizers will not grant additional cooldown reduction. This is likely designed as such to deter multiple stacking of a cost efficient item.
Only the unique/named-unique effects will not stack. Other effects provided by the item will stack.