Item Quality

Quality (or rarity) is a rating every item in World of Warcraft has, and you can read it from the color of the item's name. On equipment it links the item level, which sets how big the stats are, to the level you need to wear it. It also decides how many different stat bonuses the item carries: gray and white gear usually has none, green has one or two, and blue or better can have up to four.

• Poor (gray) items mostly drop from monsters and chests and are meant to be sold to a vendor. Poor weapons and armor have no stat bonuses and cannot be disenchanted, though some sell for decent money and some can be used for Transmogrification.
• Common (white) items are mostly materials, reagents, quest items, consumables, vendor gear and early crafted items. White gear has no stat bonuses and cannot be disenchanted, but it often does not bind, so it can be used and then traded.
• Uncommon (green) items come from random world drops, mid-range crafting and quests. They usually bind when equipped (boss and quest items bind when picked up), carry one or two stat bonuses, and most can be disenchanted.

• Rare (blue) items mostly come from dungeon bosses and dungeon quests. Boss drops usually bind on pickup but can be traded to others who could loot them for two hours, as long as they were not gemmed or enchanted. Most give a shard when disenchanted.
• Epic (purple) items let characters keep growing after the level cap. They need the cap of the expansion they came from and are far stronger than other items of the same required level. Most come from Raids, Mythic+, top crafting recipes and other endgame content; a few are world drops that bind on equip.
• Legendary (orange) items, such as Thunderfury, Blessed Blade of the Windseeker, are a step above epics, with even better bonuses and a big role in the story. They usually need a long quest chain and a large investment of materials and gold, and they cannot be disenchanted.

Artifact quality sits above Legendary. It existed since launch only for GM items, then became real for players with the artifact weapons of Legion, one for each class specialization. Heirlooms are warbound, so you can send them to your other characters; their weapons, armor and trinkets scale to the wearer's level with stats like a Rare item, and some armor even changes type to suit the class. In Legion the heirloom color changed from light gold to Blizzard blue so it would not be confused with artifacts.