Borderlands 2Shotgun Pool

Borderlands 2 World Drops are items that drop from any suitable Loot Source in addition to their dedicated sources.
There are 67 unique items in the World Drop pool, so for farming 1 of the 41 weapons it's best to seek out its dedicated Loot Source.
If you still want to test your luck, you should equip a Vault Hunter's Relic to indirectly increase your chance of a World Drop Legendary.

Suitable Loot Sources:

• Best Boss Farms: Uranus, Cassius Leclemaine, Haderax
• Best Chest Farm: Loot-Train after killing Tinder Snowflake
• All Enemies:
  Bosses, Badass Enemies, Generic Enemies, …
• All kinds of Chests:
  Red Chests, lockers, garbage containers, cardboard boxes, garbage/... piles
• The Slot Machine