Rarity refers to a classification system used for items. The more difficult to obtain and item, and the higher the quality, the higher the rarity.

JunkGrayThese items have generally no use in the game. Sold to the merchants.
CommonWhiteCommon items can be found throughout Atreia. Vendors may carry some of these items. Usually sold to merchants.
SuperiorGreenSuperior items are uncommon. They have better attributes than common items. These may be sold by Contribution vendors. Mostly sold to merchants. No longer in use.

Heroic items are harder to find than Superior items. These are often decent to equip in lower levels. Low tier instances offer them as reward. No longer in use.

FabledGoldFabled items are more difficult to come across. They have high attribute bonuses. Effective to equip at level 50, they are commonly used for levelling up or simply selling them to merchants. Low and medium instances offer them as reward. No longer in use.
EternalOrangeRare items that can be crafted or dropped from instances. Generally used as the first tier for token-exchanged gear, and viable to use for levelling upon reaching level 56. In Archdaeva gear terms, its the lowest tier of gear. No longer in use.

The rarest items in Aion. They can be dropped from instances and world bosses, which can also be crafted. Excellent to equip. Generally the tier every player aims for. Can be obtained from Dragon Lord's Refuge and most level 65+ instances. No longer in use.

Ancient Yellow The most basic of the three gear tiers. Used through the entire levelling process and basic endgame gear. Mostly obtained from quests.
Legendary Pink Middle tier of gear. Good gear to remain in during the farm for better gear. Mostly obtained from group instances.
Ultimate Red The highest tier of gear, ultimately every player's goal. Mostly from the highest tier and alliance instances.
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