Item or Monster rarity can be Normal (grey), Magic (blue), Rare (yellow) or Unique (brown). As a general rule, monsters increase in difficulty depending on their Rarity.
Item Rarity
Items can be Normal (grey), Magic (blue), Rare (yellow) or Unique (brown). Item Classes which do not have these rarities, such as Currency, have individual rarity for each item.
Magic items can have 2 Modifiers; a Prefix and a Suffix.
Rare items can have up to 6 Modifiers; 3 Prefixes and 3 Suffixes.
More powerful and dangerous enemies are more likely to drop rarer Items.
Quality
Quality grants small bonuses to an item depending on the type of item, up to a default maximum of 20%.
Martial Weapons gain 1% more Physical damage per Quality.
Armours gain 1% more Armour, Evasion, Energy Shield and Runic Ward per Quality.
Rings and Amulets have a number of possible quality types that provide bonuses to specific modifiers on the item.
Flasks gain 1% more Life and Mana recovery per Quality.
Charms gain 1% increased duration per Quality.
Skill Gems or equipment that grant Skills grant a specific bonus to their Skill based on their Quality.
Corrupted Items
Certain items can be found Corrupted or made Corrupted using a Vaal Orb, changing their properties unpredictably.
Most methods of item crafting and modification cannot be used on Corrupted items. There is no penalty for using Corrupted items.
Charms
Charms are protective trinkets you can equip that automatically trigger a defensive effect when a specific condition is met. Similar to Flasks, Charms require charges to trigger. Charm charges can be regained by killing monsters, granting charges equal to half of the monster's Power. Checkpoints and Wells completely recharge Charms when activated.
The maximum number of Charm slots is capped at 3.
Flasks
Flasks can be used to recover your Life or Mana. Flasks are not consumable, but require charges to use. Flask charges can be regained by killing enemies.
Normal enemies grant Flask charges equal to half their PowerMagic enemies grant Flask charges equal to their PowerRare and Unique enemies grant Flask charges equal to twice their PowerCheckpoints and Wells completely refill Flasks when activated. Flasks can only hold charges while in a Flask slot.
Jewels
Jewels are items that can be socketed into Jewel Sockets on the Passive Skill Tree to grant bonuses. Basic Jewels simply grant you the listed stats, while some other kinds of Jewel can have more complicated effects, such as modifying other Passive Skills within a certain radius.
Rune
Runes are Augments of Kalguuran origin and make.
Soul Core
Soul Cores are artifacts of the ancient Vaal empire and function as a type of Augment.
Waystones
Waystones are items that can be used to travel to Maps on the Atlas.
Higher Waystone tiers open higher level areas containing more difficult monsters which drop higher level items and allows the use of higher tier Atlas Passives.
Waystones can be modified to increase the difficulty and reward of monsters encountered in Maps.
Omens
Omens are Currency items that enable exclusive meta-crafting effects, allowing for more specialised crafting.
Essence
Essence monsters are powerful monsters trapped in crystallised corruption.
Breaking these monsters free allows them to be defeated, dropping the Essence that can then be used to modify equipment.
Any monsters with Essences Modifiers drop an additional Essence of that type.
Catalysts
Catalysts are Currency items that are exclusive drops from the Breach mechanic. Catalysts add Quality that affect certain modifiers on items. There are two categories of Catalyst, one that affects Jewellery and one that affects Jewels.