Unique

In Borderlands, there are a set of items known as Unique Items. These are items usually characterized as being a reward for a difficult task, and their characteristics are usually related to the quest and/or enemy that gives you the item. Unique items are characterized by a unique name (no code nor prefix), a unique color scheme, and a special ability.

Acquiring Unique Items
Most of the Unique items in Borderlands are acquired in one of 2 ways:
 * 1) The item was previously wielded by a unique enemy. The earliest example is Bone Head's Bone Shredder.
 * 2) The item is a reward for a quest. For example, T.K. Baha will give you his T.K.'s Wave after completing T.K.'s Life And Limb. The weapon will almost always be related to the Quest/Character that gives it to you, though there are exceptions.

Note that in both cases, these are always guaranteed drops. Exceptions include the Lady Finger, which is found in a quest-related stash, and The Chopper, which has no guaranteed drop location, and can only be farmed.

Farming Unique Items
During a normal play through of Borderlands, almost every unique item can be acquired once, with no particular effort. It is when trying to farm a Unique item more than once that things get more complicated. The re-availability of unique items can be broken down in several groups:
 * Respawnable Unique Boss Drop: For example, Bone Head and Sledge will always drop their Bone Shredder and Sledge's Shotgun. Re-acquiring the unique item simply involves finding and killing the enemy again.
 * Quest Reward: A quest reward can only be obtained once, making this items a theoretic 1-time only drop. Thankfully, in most of the case, there is a unique monster related to the quest that will have a chance to drop the unique item. For example, after completing T.K.'s Life And Limb, and obtaining T.K.'s Wave from T.K. Baha, Scar will also start dropping T.K.'s Wave. These drops are not guaranteed though, and require more effort. Almost all quest items can be re-acquired this way, except for Chiquito Amigo, Athena's Wisdom and The Spy (to a certain degree). Lady Finger and The Chopper fall in this category.
 * Non Respawnable Unique Boss Drop: Most notably King Wee Wee's Wee Wee's Super Booster. Unfortunately, these items can only be acquired once. To "farm" these items, it is recommended to save the Unique Boss for play through 2.5, to increase the item's level. The farming then consists in acquiring the item, and not-saving if the item is not satisfactory.

Characteristics
Unique weapons bypass Borderland's classic weapon generation mechanics in that they often have restrictions on their parts. This means that Unique weapons usually don't have as large a specter of characteristics as other weapons. For starters, all unique item will have a unique material. This material will give it a special color scheme, and sometimes also change its characteristics. Like Legendary items, Unique items will also have a predefined part from which the special effect derives. Finally, there will be the part restrictions. For example, Sledge's Shotgun will always have a blade, will always have a 2 clip magazine, and will never have a scope.

Rarity
Unique items don't have any special rarity. They are more often than not Blue, but can also be Green, Purple, or even Legendary.

Mixing with Legendaries
As long the Unique item's part restrictions don't forbid the Legendary item's part, and the manufacturers match, than it is not impossible for Borderlands to generate Unique Legendaries. For example, Atlas's Ajax's Spear Combat Rifle can spawn with an accessory, and the Atlas Legendary Combat Rifle, the Ogre, gets its effect from its accessory. As such (albeit extremely rare), it is sometimes possible to find an Ogre Ajax's Spear.

Whenever a Unique and a Legendary merge, the Legendary name overrides the Unique name, the item code appears, but there will not be any prefix. For example, an Ajax Spear will become an AR590 Ogre.

Notable examples include:
 * Dahl's Hornet Dove
 * Tediore's Savior Bone Shredder